Geoptik camera lens setup.

[ollypenrice]

Martin asked if I could post a picture of the setup I used for part one of my envisaged Orion mosaic so here it is;

On the left, an Atik 4000 mono. On the right a Samyang 85 prime lems supplied by Telescope Service. And in the middle, the orange and black device, a Geoptik Canon fit adapter from Altair Astro.

The Geoptik is simply bolted to one of the camera holders built into the ST80 tube rings rings which came as standard with the guidescope from FLO.

The central black part accepts the camera on the left and the lens on the right. The large right hand orange lockring locks the lens in place as you would expect.

The the similarly large orange lockring on the left is a rather expensive (£39) 'variable spacer' - but lockring would be a more accurate term. It allows a very small amount of adjustment to get the chip distance right. You thread the camera in and out till the distance is correct and then lock it with the orange ring. This is also handy for framing your picture because you can lock the camera in any orientation. (My chip is square so a 45 degree turn covers all eventualities and will not throw out the chip distance enough to matter.)

The central, black, part of the Geoptik adapter is a little mysterious in that it accepts a 1.25 inch filter. That is not mysterious in the least but what is odd is that the filter threads not directly into the adapter but into a ring which itself is threaded into the adapter. If this were a 2 inch thread it would be self explanatory but I don't think it is. (I don't want to lose my camera orientation or flats so I can't open it up to check.) Anyway it does mean you can fiddle around to get your filter close to the chip.

Changing filters is a fiddle and not practicable for RGB-mono work in my view. I would not do it in the dark, for sure. However, for NB or one shot colour it is fine.

Canon lenses have a chip distance of 45mm, the Geoptik takes 19, so you have 26 to find including the back distance of your camera. I use a slightly extended M42 fitting on my Atik camera and I'm just right with room to fine tune.

The lens; wide open it is at f1.6 but, unless I have my chip spacing miles out, I would say that an astrophotographer would want to run it no more open than f4, certainly on my chip size. Below that the edge distortions are huge. However, at f4 it is pretty good and one more stop down would still be quite fast and even tighter. I used f4 in Ha but mght stop down a bit more when shooting colour. Of course I'll be doing this in the Atik 4000 OSC, to be sure.

All in all I think it makes a nice widefield setup and it means that any visiting Canon lens owners can plug and play very easily. Above all it just bolts onto either of my ST80 guidescopes in a Jiffy.

Olly

[Beyond_Vision]

Thanks for posting that Olly

[Photosbykev]

The Samyang 85mm lens gets a good write up for normal photography, it should be quite at home shootng the stars.

[MartinB]

Thanks for this Olly, very neat, looking for something like this for use with my QHY8

[simon84]

What a lovely setup. Who needs big mounts with setups like that. Now all it needs is an LCD screen on the back and a trigger and you can take your holiday snaps with it aswell.....

[Dangerous-Dave]

Changing filters is a fiddle and not practicable for RGB-mono work in my view. I would not do it in the dark, for sure. However, for NB or one shot colour it is fine.

This was certainly the main problem I experienced using my mono H9 with my Leitz apo lens. The answer is of course to use a lens with a longer register, such as Hasselblad or Pentax medium format, so plenty of room to fit a filter wheel in there.

[ollypenrice]

Good point, Dave. What I will do next (clear from tomorrow, they say) is slightly alter my chip distance to see if I can get the lens to run faster than f4 and still give clean stars. If not I may even think of coming down a further stop once using full broadband RGB. But the present project is Ha for a while to come.

Olly

[davew]

Oh no, it's that pedant again....

Just to help you decide. If you've worked out your distance using 45mm as the Canon lens register, you'll find it's actually 44mm

You look to have a killer set up there. Good luck with Orion.

Dave.

[ollypenrice]

Thanks Dave. Actually that's not good news because I can't come in much without a lot of faff. However, since my focus ring is set short of infinity does that suggest that I am too close still? Urr, struggling with this one!

Olly

[Photosbykev]

If you aren't achieving infinity the chip is too far away from the lens

[davew]

I think they need to be as close to correct as you can get them. If you are quite close to infinity I would say you're ok.

Throw an Ha filter into the mix and I have found here that the focus point moves. Even a slight amount when you change focal ratio. Say f2.8 to f4. I used to think that I would open a lens right up, focus and then close down. Not any more.

A 50mm f1.8 lens I have focuses at 3Mtrs. A 105 f2.8 focuses very close to infinity. Go figure that out.

Dave.

Cross post with Kev. I think you're correct

[ollypenrice]

More thanks for the hints.

Olly

[Coco]

Great write up Olly..

[johnrt]

Very interesting - this chap makes something very similar. Anyone know anything about his stuff? Phil Dyer, Mintron Astro Video Cameras, accessories, adapters for Telescopes, DLSR lenses, CCD cameras, video cameras, webcams and microscopes

[davew]

I don't know the Phil Dyer specifically but it looks similar to the Mogg adapter. I think some of them are turned out of Delrin ??

If this is one of them, they have a habit of sagging if the lens is heavy. Check that out. Olly's is a proper jobie.

Dave.

[johnrt]

Thanks Dave, that was the sort of info I was after.

Incidentally when using an adapter like the one here and a canon lens, how would you set the aperture rings in the lens, modern ones are all controlled via the dslr itself.

I don't know the Phil Dyer specifically but it looks similar to the Mogg adapter. I think some of them are turned out of Delrin ??

If this is one of them, they have a habit of sagging if the lens is heavy. Check that out. Olly's is a proper jobie.

Dave.

[ollypenrice]

Thanks Dave, that was the sort of info I was after.

Incidentally when using an adapter like the one here and a canon lens, how would you set the aperture rings in the lens, modern ones are all controlled via the dslr itself.

I gather that you set it electronically on a Canon camera then remove it and put it on your CCD. The iris stays put. I have not tried this because my Samyang is manual.

Olly

[Coco]

Olly, is there an internal thread option for a filter?

.

[ollypenrice]

Yes. It is all a bit mysterious. Inside the adapter is a ring which threads in and out. This ring is itself internally threaded for a 1.25 filter. Why you don't just thread the filter into the adapter itself I don't know. And no, it isn't a 2 inch filter thread if you take the ring out; I'd thought of that as well!!

So you can change the filter but it is a pig of a job and not, to my mind, one to do at night and in a field. You can take off the lens or the camera to change filters but neither is easy and getting the filter out is far better off the mount.

It would be possible to make a filter wheel type adapter but it seems no-one does. You might need unmounted filters to get the width down. So what I do is use the OSC then maybe add an Ha layer after switching to the mono Atik 4000.

The QSI 285 with internal wheel can, I think, take camera lenses.

Olly

[Coco]

Ok, shame as it looks well made.

I was looking at the TS version too, it has a filter drawer but am not sure if this would pull the filter too far away from the CCD face.

.

[riklaunim]

There is some backfocus left in that Geoptik solution, so a filter drawer may fit in.

In my case I'm experimenting with old M42x1 lenses:

And it fits together nicely... Real world images ToDo soon

[Coco]

There is some backfocus left in that Geoptik solution, so a filter drawer may fit in.

In my case I'm experimenting with old M42x1 lenses:

And it fits together nicely... Real world images ToDo soon

Looks good, nice and neat, the problem is the 383 has 17mm ccd to nose end...

[383 = 17mm] - [filter drawer 15mm ] - [adapter 14.5] = 46.5mm which is 2.5 mm out, am not sure if it will gain infinity focus? And this is assuming everything fits flush and has no radius edges ..

anyone?

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