SM60 Cental obstruction issues

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Stone

SM60 Cental obstruction issues

Post by Stone »

Hello everyone, just taken delivery of a new SM60II DS with BF5. Now this comes as standard with the 25mm cemax, but try as I might I cant view with this eyepiece without having a very prominent central obstruction shadow and ghost/red reflections all over the place. Is this normal? The only way I get a sensible view is to drop in a 20mm or 15mm eyepiece and then navigate away from 'shadows'. Having done that, the image is superb! My first doublestack.... :) Is this just life with a BF5 or something more serious? Apologies for my non-tech descriptions...
Many thanks for any help.
Chris


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Re: SM60 Cental obstruction issues

Post by Merlin66 »

Chris,
Welcome on board.
I hope that someone with a similar set-up will chime in and assist you..
I have the older version of the Solarmax and have a SM60 etalon upfront as a double stack.
There should be no issue with the central obstruction (a bit like a secondary mirror in a SCT etc) it's well away from focus. The ghosting however may be associated with the tilt of the front etalon. Try using the T-max adjuster to move the ghosts off to one side.
(It may be you're getting confused between the "obstruction shadow" and the visible sweet spot where the contrast varies across the field of view?)
Hope this helps.


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Stone

Re: SM60 Cental obstruction issues

Post by Stone »

Hi Merlin 66, many thanks for your reply. I've done loads of tuning and focussing alternatives but with the 25mm (for full disk & brightness) I still get a 'shadow/dark spot' approximately 1/4 solar diameter in the centre of the image. Tuning, etc. to get the sweet spot at higher mags is all fine. Optimum balance of brighness/contrast/detail/no obstruction seems to be at 15mm at present. Will a BF10 make any difference?
Thanks
Chris


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Re: SM60 Cental obstruction issues

Post by Merlin66 »

I usually use a TV 10.4 plossl on my SM60 DS. It also has the BF10.
I think the 25mm may be too low a power (x16) for the BF5....
What's the minimum magnification which gives a full disk? (AFOV/magnification..a 50degree eyepiece, the mag would be x100 for a 1/2 degree FOV...with a 400mm fl this would be a 4mm eyepiece! so a 8-10mm would give nice FOV results?)


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Re: SM60 Cental obstruction issues

Post by Montana »

A very warm welcome to you Chris!
I might possibly know what you mean. I have 2 of these 25mm lens, one came with my PST and the other with the CaK PST. I just cannot use them, no matter where I put my eye I get a dark shadow spot, however if you are really careful and gradually bring your eye out to a distance of around 3cm from the eyepiece, suddenly everything snaps in to view but vanishes if you wobble just a moment (which is impossible not to wobble). Also at that distance it is difficult to concentrate on the image. My husband initially refused to look at the Sun for about a month after I first got the PST as he refused to sit and desperately try and view. I then got a Pentax zoom lens and all problems solved. Really I should put these 2 lens in the bin but I just don't have the heart.

Alexandra


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Re: SM60 Cental obstruction issues

Post by florencior »

Welcome Chris.

I already sold my SolarmaxII60, but i experienced the same as Alexandra when i had it (and i was using a BF15), till i found thet the image showed right when i just moved away from the eyepiece, try it.


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Re: SM60 Cental obstruction issues

Post by Spectral Joe »

I can explain (optically) what is happening: the exit pupil of a telescope is an image of the entrance pupil, which is the aperture of the objective. If the objective has a central obstruction (or there is one close to it) then the exit pupil will have one as well. If the exit pupil is exactly at your eye's entrance pupil then the obstruction can not be imaged onto your retina, but as the position of your eye's pupil moves away from this optimum position you are able to perceive the central spot. This also accounts for the "tunnel vision" effect of having your eye too close to or far from the eyepiece. In that case you are perceiving the outer edge of the objective. The telescope reimages the objective onto your eye, and vice versa, provided your eye is at the correct position.


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Re: SM60 Cental obstruction issues

Post by marktownley »

Sorry to say but the 25mm is a complete waste of time with these 400mm fl scopes - I don't know why coronado ship them, but they do. I find 15mm a nice / optimum fl eyepeice.


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Re: SM60 Cental obstruction issues

Post by brianb11213 »

I don't know why coronado ship them
IIRC both my Ha and CaK PSTs came with 20mm Kellners ... which I no longer have as they were pretty well useless .... 18mm BGO is good if you really need a power that low but 12.5mm (again BGO) is the one that I used most often with my Ha PST (400mm f/l) when I had it. 9mm is good for higher power views, beyond that I found the PST started to struggle but some people like to use powers higher than I foind acceptable. I don't use an eyepiece at all with by CaK PST as I can see nothing at all at that wavelength.


Pedro

Re: SM60 Cental obstruction issues

Post by Pedro »

I am interested in buying 12mm and 25mm Cemax eyepieces (I have the whole set and want to buy the pairs). I want to use these eyepieces with my WO binoviewer. Anyone interested in selling?

Alexandra don't send it to the bin... Most of the times I use zoom eyepieces (Pentax, Baader, Vixen) but I also like to use the WO bonoviewer to view the sun.

best


brianb11213

Re: SM60 Cental obstruction issues

Post by brianb11213 »

I am interested in buying 12mm and 25mm Cemax eyepieces.
They're pretty ordinary Plossls ... good quality Plossls like those sold by Televue, or orthoscopics, will do just as well. Baader Genuine Orthos are not expensive, available in 12.5mm but not in 25mm or anything near, but "volcano top" orthos (which are cheaper) should do OK.


Pedro

Re: SM60 Cental obstruction issues

Post by Pedro »

Hi Brian:

You're right and I have a couple of pairs (20mm and 10mm). However I'm interested in using Cemax pairs (25 and 12mm). I already have two 18mm Cemax eyepieces.

best


Stone

Re: SM60 Cental obstruction issues

Post by Stone »

Mmm... Thinking of maybe an 11mm Nag. My Delos 6 is good with it but a little dark. Wish I had the dosh for a Delos 10... :huh:


Stone

Re: SM60 Cental obstruction issues

Post by Stone »

Sounds like exactly what I'm experiencing!


Stone

Re: SM60 Cental obstruction issues

Post by Stone »

Hi Florencior, Tried, but still a no go with a 25 or 20, only gets reasonable at 15mm. Does anyone know if the Lunts have this central obstruction issue?


Stone

Re: SM60 Cental obstruction issues

Post by Stone »

Thanks Joe, do you happen to know if this is also a factor with the Lunts? I read somewhere they dont have a central obstruction??


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Re: SM60 Cental obstruction issues

Post by Montana »

Sorry Pedro, I would definitely have sold them to you but I have just had a look, I have 2x 20mm ones :( gathering dust.

Alexandra


Pedro

Re: SM60 Cental obstruction issues

Post by Pedro »

Hi Alexandra:

Thanks anyway. I will keep looking for a second 25mm and 12mm Cemax eyepieces,

best regards


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Re: SM60 Cental obstruction issues

Post by marktownley »

Mmm... Thinking of maybe an 11mm Nag. My Delos 6 is good with it but a little dark. Wish I had the dosh for a Delos 10... :huh:

Simple plossl eyepeices work best with Ha...


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Stone

Re: SM60 Cental obstruction issues

Post by Stone »

Do you think then maybe a TV 10 or similar? Anyone got tips?


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Re: SM60 Cental obstruction issues

Post by Merlin66 »

With the SM60 DS/ ED80 I find the ol' TV10.4mm plossl to be pretty good.


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Re: SM60 Cental obstruction issues

Post by marktownley »

I use a TV 15mm plossl all the time now with my DS40, i'm pretty close to buying a 11mm TV plossl for Ha too...


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Re: SM60 Cental obstruction issues

Post by PEterW »

Lunt, no problems with dark holes with my baader 8-24mm zoom, didnt see envy with it and my PST or the ?12mm standard eyepiece that came with it. Sounds like a bad case of kidney beans, and I thought it was only naglers that suffered from that? As suggested, reduce the focal length and you ought to get good views, the central etalon spacer is there to maintain the precise alignment and keep the unit robust, it will not affect the views, though some may claim that unobstructed are better (same sort of argument that gift buffs have....!)

Cheers

Peter


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