My mini stage 2

[JohnM]

Since I'm now putting together a 4"and dismounting the old 6" this thing usually rides on top of I had a chance to get a good photo of it removed from it's own rings and plate.
It'll probably be a while yet I guess before I get the parts to mount the 4, so I'll probably mount this by itself again.

[marktownley]

Cool looking beastie! 8)

[swisswalter]

Hi John

what a mod :

[vikeljay]

How did you connect the tube to the focuser? Is there an adapter for that? What other mods did you have to make for this to work? What about how you tune the etalon. I do not see the tuner in the photo. I want to try something similar. Thanks.
Jim

[JohnM]

The focuser is a model to fit on the back of an SCT, I used an inexpensive one from Scopestuff.
I used two 1/2 inch SCT extensions to attach the etalon to the focuser, the thread is close enough.
After a lot of assembly/disassembly the threads began to come loose. Either use some teflon tape or a little medium strength thread locker to be sure it won't fall apart on you from a bump or such.
The etalon is tuned normally, I just never bothered to put the rubber band grip back on mine.




Those 2 marks I made on the second photo are 200mm apart. From the BF to the front of the etalon.

[Allcart]

Hi John, have you used the 5mm blocking filter from the pst or have you used a different one.?

[JohnM]

I always got the best results with the PST 5mm.
I have a 10mm supplied by Denk/Spectrum, but it never worked right with this setup.
I had a chance to slip it in the 4" today for a minute and it seemed to produce better there.

[Allcart]

Yes I expect that the 5mm works fine with a 40mm objective but the 10mm is better suited to the larger aperture. Seeing your mini stage 2 has given me a clue as to what I can do with my pst spare blocking filter and parts.

[JohnM]

Is it only aperture related or does FL come into play?
Lunt lists various FL suitable for their different sized BFs.

[JohnM]

I forgot to post a pic of what I use to hold this creation on the mount.
A couple rings for a 50mm finderscope and an old 8" dovetail fits that PST tube perfectly.

[vikeljay]

Where did you get the 50mm finder scope rings? I have been looking for some. Thanks.
Jim

[astroshot]

Am in correct in saying that the 200mm distance should be measured from the etalon to the ccd camera, rather than the BF?

[JohnM]

Maybe so, but that's basically focus.

[marktownley]

Am in correct in saying that the 200mm distance should be measured from the etalon to the ccd camera, rather than the BF?

Yes

[astroshot]

Thanks.
Next question then is to do with the use of a barlow.
If I were using a PST and inserted a barlow lens between the camera and ccd chip, I would need to adjust focus.
Therefore, am I correct in saying that when using a stage II mod, if I want to use a barlow lens, I should first focus the system without a barlow, insert the barlow and finally adjust the distance between the chip and etalon until it refocuses. The point I am getting at is that at no stage does the main telescope's focus position change. Is that correct?

[marktownley]

The point I am getting at is that at no stage does the main telescope's focus position change. Is that correct?

Yup, that's right

[RobBower]

That is the hard part! I guess once you find the perfect match you tend to keep it there?

[JohnM]

I've never been able to figure out actual distance versus optical distance using barlows.

[RobBower]

Im thinking its more t thread extension tubes between the etalon and diagonal.