Will this crazy 'Mod' work? Your constructive criticisms much appreciated.

Ken Crawford · Post by **Ken Crawford** » Sat Dec 03, 2011 6:29 pm

So PCX like these?

http://www.edmundoptics.com/products/di ... c#products

Post by **marktownley** » Sat Dec 03, 2011 7:26 pm

My plan is to use it in the configuration as per Rogerios http://www.astroimagem.com/Mybestimages ... daicon.jpg rather than the configuration David Evans proposed at the start of the thread. The 50mm should work in this manner, my plan would be to mount it on the front of my DS40 etalons in a folded light path @ 500mm behind the fp of the meade...

Post by **marktownley** » Sat Dec 03, 2011 7:49 pm

Yes, the convex element design would be better - would this have to have the same focal ratio as the primary objective?

Marcon · Post by **Marcon** » Sat Dec 03, 2011 9:03 pm

Hello
First I want to thank Pedro Re for inviting me to join this list. Here you can discuss changes in the telescope without danger of being excluded. Thanks Stephen!

My system is simple. Do not use rejection filter. The important thing is to always work with f/10 throughout the system. The small refractor is about 500mm focal length (f/10), the PCX lens also has the same focal length and 50mm diameter. This is a collimator lens and produces a beam parallel to the etalon. Formerly used an SM40, but recently replaced it with a Lunt LS50 BF1200 filter.

The PCX lens is obviously 500mm away from the image generated by the large refractor, a 200mm diameter and 3000mm focal length. It's an old AS200 Zeiss.
To reduce the heat on the etalon, I use an aluminum plate with a small rectangular window about the size of the CCD chip at focal plane. Thus, much of the image is retained on the plate and only through what will serve for the camera.
The PCX lens works perfectly because color correction is not necessary and is not observed spherical aberration or coma.
The secret is to keep all the lenses at f/10 or f/15 and use aluminum foil with a window to heat retention.
For images, I use the camera Lumenera LU075M capturing 3000 frames at 50 fps. I usually do a central image and the four quadrants, then assembling the mosaic with iMerge software.

Best Regards and clear skies

Rogerio Marcon

Post by **solarchat** » Sat Dec 03, 2011 9:07 pm

Rogerio! The worlds best solar imager...hands down!

WELCOME!

Ken Crawford · Post by **Ken Crawford** » Sat Dec 03, 2011 9:09 pm

Thanks for joining up and explaining your system!

One question, would adding an ERF to the front to limit the heat and not use the aluminum plate be ok?

Pedro · Post by **Pedro** » Sat Dec 03, 2011 9:13 pm

Welcome Marcon and thanks for your post. Everything is more clear now (at least to me).

best regards
abraço amigo

Post by **marktownley** » Sat Dec 03, 2011 10:11 pm

Welcome Marcon and thanks for your post. Everything is more clear now (at least to me).

best regards
abraço amigo

Yes, indeed, thank you. The whole f-ratio thing makes absolute sense.

Marcon · Post by **Marcon** » Sat Dec 03, 2011 11:09 pm

Thanks guys
Ken, I think that it is possible to use an ERF. I do not have one and I could not test this alternative.
The disadvantage of my system is its size. The total length exceeds 4 meters and I used a flat Zerodur mirror to bend the tubing in half because it would not fit in the observatory.

Blue Skies

Rogerio Marcon

Post by **marktownley** » Sun Dec 04, 2011 5:28 pm

OK, all this talk really got me thinking last night, and after ordering my lens i decided to try and mechanically configure all the parts I would need to make a system the same as Rogerios. The good news is that it seems pretty easy: In order to bend the beam path through 180o I was able to use two 2" diagonals, this also allows me to align the beam from the big frac with the etalons. The 50mm f10 objective would sit (at correct distance) between the 2nd diagonal and the etalons on the second scope - this would mean the etalons receive a collimated beam. I've took some pics so you can see what I mean...

DSCF2345 by Mark Townley, on Flickr

DSCF2346 by Mark Townley, on Flickr

DSCF2344 by Mark Townley, on Flickr

DSCF2343 by Mark Townley, on Flickr

DSCF2342 by Mark Townley, on Flickr

DSCF2341 by Mark Townley, on Flickr

DSCF2340 by Mark Townley, on Flickr

If this works out I will be one happy bunny as will be able to work at 120mm aperture 0.5a - that could be fun!

swisswalter · Post by **swisswalter** » Sun Dec 04, 2011 7:05 pm

Hi Mark

very funny see my pic of almost the same. I'v gotten an first light but never reached good focus

first light

have fun and please report

Post by **marktownley** » Sun Dec 04, 2011 7:40 pm

Great minds think alike Walter!

What is the big frac you are using there? And is the lil' scope a 60mm lunt?

The focus in the image seems ok to me - would you say the focus issue was a combination of large aperture and low sun / poor seeing or as a result of how things were set up mechanically?

Pedro · Post by **Pedro** » Sun Dec 04, 2011 7:47 pm

Nice setups Mark and Walter. Please keep us posted.

best regards

swisswalter · Post by **swisswalter** » Sun Dec 04, 2011 8:04 pm

Hi Mark

thank you very much. You are guessing right. It is my 152 Apo f/8 and the LUNT 60. In front of the LUNT 60 there was the edmund lens placed.

I think my wodden construction was not aligned correct enough to give a good focus. Of course using a scope mit 152 mm is not for everyday seeing.

On top of that I did not play / optimize the distance 2nd diagonal to LUNT 60.

I'm so happy that we can discuss these things here in the forum.

Think about the consequences we did that withhin CN

Post by **marktownley** » Sun Dec 04, 2011 8:44 pm

Hi Walter, thanks for the info!

Looking at your picture all the angles of dangle look ok to me, I wonder if the focus issues you were having were just a result of that 152mm aperture?

I have been thinking about the spacing of the edmund lens with respect to the focal point myself; I initially thought I would have to place it 500mm behind the focal point, however as this is a 50mm f10 it would give me a 50mm collimated beam - I would be wasting light (and resolution?) here as my etalons are 40mm, so, have decided to mount the edmund lend ~350mm behind the focal point; this will give me a collimated beam ~35mm diameter, which is a much better match for my etalons and also gives a bit of leeway incase of slight mechanical misalignment...

I'm glad we can talk about this too - we would have all been banned on CN had we even dared think it...

Post by **marktownley** » Sun Dec 04, 2011 8:49 pm

Incidentally, this is the edmund lens I bought

http://www.ebay.co.uk/itm/230446149304? ... 1497.l2649

A bargain I think!

swisswalter · Post by **swisswalter** » Sun Dec 04, 2011 8:58 pm

Hi Mark

very interesting. I bought another lens. I'll show it later to you and the members here. Rogerio helped me setting up this scope. (thanks again Rogerio)

It's time to me to hit the pillow

robert · Post by **robert** » Sun Dec 04, 2011 9:01 pm

I think you need the lens to be 500mm beyond the image plane to get parallel rays, at 350mm they will be diverging
Robert

Post by **marktownley** » Sun Dec 04, 2011 9:14 pm

I think you need the lens to be 500mm beyond the image plane to get parallel rays, at 350mm they will be diverging
Robert

I reckon you're onto something there Robert, my brain is coming up with ideas quicker than i'm reasoning with them. Maybe the 40mm f10 lens from my CaK PST would be a better match to my etalons - hmmm...

Post by **marktownley** » Sun Dec 04, 2011 11:59 pm

The 40mm CaK PST objective (and hacked gold tube) seems to be a nice tool for this job: geometry wise it fits in nicely and seems to be just the right size. The white tube sits over the etalons and the end of the PST objective to line everything up...

DSCF2348 by Mark Townley, on Flickr

DSCF2347 by Mark Townley, on Flickr

Now all I need is first light...

Ken Crawford · Post by **Ken Crawford** » Mon Dec 05, 2011 12:55 am

Amazing ~ LOL that is going to be interesting. Looking forward to your first light.

robert · Post by **robert** » Mon Dec 05, 2011 9:37 am

Amazing ~ LOL that is going to be interesting. Looking forward to your first light.

me too! B)

davidevans · Post by **davidevans** » Mon Dec 05, 2011 10:27 am

I really think we are on to something here guys....

I can see us all ending up with large solarscopes!

Great teamwork.

Marcon · Post by **Marcon** » Mon Dec 05, 2011 11:43 am

Yes, it will work. My first prototype used two prisms. Later I switched to a single plane mirror.
My system was originally based on the optical telescope OSPAN (ISOON):

http://nsosp.nso.edu/ospan/images/ospan-optics.gif

This is a way to get high resolution with small filters. The disadvantage is the size of the telescope.

Clear Skies

Rogerio Marcon

Post by **marktownley** » Mon Dec 05, 2011 5:02 pm

Excellent, glad you think it will work Rogerio, this reassures me!

If the only caveat is the size of the scope then this is something I will happily live with, my mount regularly is 'double scoped' and is happy with the weight so all is well there. I really can't wait to try 118mm @ 0.5a, I have a feeling the view compared to the 40mm i'm used to is going to blow me away!

davidevans · Post by **davidevans** » Tue Dec 06, 2011 9:14 pm

I would like to recommend an online optical ray tracer applet

http://www.arachnoid.com/OpticalRayTracer/index.html

The applet can also be downloaded to run as a local application from your hard drive.

Regards,

Dave

swisswalter · Post by **swisswalter** » Tue Dec 06, 2011 9:34 pm

Hi David

thank's I'll have a try

Derek Klepp · Post by **Derek Klepp** » Wed Dec 07, 2011 10:28 am

Ok after reading all this I'm beginning to understand whats going on. Mark and Walter when you've worked it out is it posible to produce a line drawing with all lenses mirrors filters etc and measurements as well as the light path. That is does it stay parallel all the way or converge then diverge on its way to the focal point. Also is there a focal point near the base of the first scope or is this nullified and the rays remain apart until the focus of the second scope.?,
Derek

Marcon · Post by **Marcon** » Wed Dec 07, 2011 11:44 am

Yes Theo, the ideal would be to have a PCX lens at f/15 getting the beam with a diameter of 50mm, but at f/10 works well. Because the source is not as punctual as a star but a small rectangle, the parallel beam is slightly wider than the 33mm. There is no light loss.
You could not use an f/D greater than 15 for the PCX lens because it would result in loss of part of the beam.

Regards

Rogerio Marcon

swisswalter · Post by **swisswalter** » Wed Dec 07, 2011 6:18 pm

Hi Derek

thanks for the job :-). I have given up the system a year ago because I got a LUNT 100 which is great and have sold my LUNT60 with the 50 double stack. So I can't go this way again.

In the meantime I'm working on a 127 and 152 FH both f/10 with eighter the PST etalon or the new Ha filters from Robert Johnson. The Ha filters from bob are not yet mounted, because the tilting mechanismen from Israel have not yet arrived.

Winterime is experimental time, so I'm looking forward to interesting news :-) I'll report in that forum. Where else :-)

Post by **marktownley** » Wed Dec 07, 2011 8:20 pm

Hi Derek,

If this is successful as I hope it is will definitely get some schematics up - but, bear in mind, this will be specific to my particular optical configuration, though, as I understand easily adaptable and configurable to different optical systems...

All being well I hope to test it on saturday morning in my 'hour window' - will keep you updated...

Post by **Merlin66** » Tue Dec 13, 2011 2:46 pm

I have images somewhere of a EC90 (El Cheapo) 90mm folded design using a SM40 etalon (later double stacked with a PST etalon)
I found the double diagonal trick to be a problem...they didn't give me 180 degrees.
I used a couple of 50/50 front surface mirrors ( cut down the heat loading and fully adjustable)
The first prototype was based on a TV Big Boy x 2 barlow to give the necessary parallel collimated beam to the SM40 but again I found this to be a poor decision...the double positive lens is definately the way to go.
We've also been playing with a LADS and LASS concept - Large Aperture Double Stack and Large Aperture Single Stack where a sub-diameter ERF is used.....

Post by **marktownley** » Tue Dec 13, 2011 8:18 pm

Great to have you here Ken!

Hopefully the weather will oblige over Christmas and will be able to test this thing out. I hear what you're saying about the 2 diagonals not being 180 deg and can imagine the issues it will create - couple of mirrors could be a thing to look at...

You got any details on LADS and LASS you could link to? There are alot of people here who would find it interesting

Post by **Merlin66** » Thu Dec 15, 2011 8:10 am

Most of the discussions were on the SGL forum in the UK
http://stargazerslounge.com/diy-astrono ... scope.html

Post by **marktownley** » Thu Dec 15, 2011 2:02 pm

Some very interesting discussion on that thread, thanks for the link Ken

Post by **marktownley** » Sun Mar 04, 2012 4:58 pm

Just to give an update on this: I tried a 'first light' with my setup last weekend however could not acheive focus. Believe the issue to be the exact position of the collimating lens prior to the etalon. As soon as sun is out for long enough I will have another shot...

peter drew · Post by **peter drew** » Sun Mar 04, 2012 6:45 pm

I was naturally really impressed by Rogerio's results and had been contemplating a larger aperture than my original 90mm PST mod. I have a 220mm F12.5 achromat refractor and experimented with a 80mm ERF before the PST combination. The results were outstanding visually but the ERF got uncomfortably hot. I eventually rigged up a stand alone cold air blower feeding into an aperture through the side of the main tube, this kept the ERF reasonably cool for the duration of the observations. To try and work around this complication I placed a 140mm ERF as close to the objective as possible without vignetting the focal beam, at this position there was no noticeable thermal problem. I would not advocate this aperture for regular use in the seeing conditions we usually have in the UK. I am at the moment trialling a 150mm F10 PST mod with a 110mm Baader ERF as a subdiameter unit and a BF15 to improve the field of view. The Istar objective was purchased brand new, all other components were good secondhand, total cost £1450.

Pedro · Post by **Pedro** » Sun Mar 04, 2012 7:09 pm

Very interesting Peter. Do you have images of your mods?

best regards

astroshot · Post by **astroshot** » Sun Mar 04, 2012 8:03 pm

Out of curosity, where can one get 8-10" acro refractors for large aperture h-alpha observing / PST mods?

Post by **marktownley** » Sun Mar 04, 2012 8:06 pm

Out of curosity, where can one get 8-10" acro refractors for large aperture h-alpha observing / PST mods?h

http://www.istartelescopes.co.uk/page_2413941.html

Quite reasonable for the money i think...

astroshot · Post by **astroshot** » Sun Mar 04, 2012 8:57 pm

Thanks Mark.

At what point is it more practical to use a Newtonian with an f10 primary mirror blank i.e. no coating? IIRC, it would still reflect a small percentage of light.

Post by **marktownley** » Sun Mar 04, 2012 10:26 pm

Thanks Mark.

At what point is it more practical to use a Newtonian with an f10 primary mirror blank i.e. no coating? IIRC, it would still reflect a small percentage of light.

Indeed, the law of diminishing returns starts kicking in, or, in my case poor seeing is the governing factor...

Post by **marktownley** » Tue Mar 13, 2012 8:44 pm

Just to give an update on this: I tried a 'first light' with my setup last weekend however could not acheive focus. Believe the issue to be the exact position of the collimating lens prior to the etalon. As soon as sun is out for long enough I will have another shot...

Actually bothering to do some proper 'measuring' shows my spacing of the collimating lens to be the issue. Just need a sunny weekend day now when I don't have any chores to do...

Post by **marktownley** » Tue Mar 27, 2012 10:08 pm

Actually bothering to do some proper 'measuring' shows my spacing of the collimating lens to be the issue. Just need a sunny weekend day now when I don't have any chores to do...

Tried again on this mod, but the collimating lens was still sitting too far from the position it needs to be; made a 'custom' adapter for the collimating lens today which should get it to the position it needs to be. So far the 'beam' coming out of the collimating lens, while close, is still not a 100% parallel beam. Onward and upwards...