Adaptor for telephoto lens's OR small scope?

[swag72]

While I am waiting for my Atik 314L I am thinking that I will miss a little the more wide field stuff, that I suppose I would have to mosaic for. So this got me thinking. I was looking at purchasing a Geoptrik adaptor, so that I could use the Atik with my Camera len's. I am specifically thinking of larger targets that won't fit in my current FOV of the SW 120ED + 0.85 reducer and the Atik.

I have a side by side bar, so wondered whether to get a small scope, such as the Borg 45II here.

I would welcome some thoughts on which would be a better route to go down and why. I'm really not sure at the moment.

[Digz]

I really like the idea of using dedicated CCDs with camera lenses for widefield astrophotography. I guess if you have some decent glass then you can get some good images.

Cant really answer your question though, but Im interested in what the answers maybe and whether there are any alternatives to the geoptrik.

[Psychobilly]

The downside of using camera lenses is the touchy focusing but thats made a lot easier using something like the TS micro focuser...

http://stargazerslounge.com/member-equipment-reviews/134080-ts-focus-contraption.html

If you want to do a quick test then a spare rear cap for the camera lens and a 35mm film canister can be made into a quick and dirty 1.25" adaptor

Peter...

[swag72]

Cheers Peter - I had seen that focusing thing before.

Still can't decied what is best - What would you go for if you had to make the choice?

[Psychobilly]

If you have some nice glass already (and I know you do) I would probably go the Genoptik route... especially if your using a smalller sensor camera (which is your plan)

Have you seen TJ's (Tim's) pics with the camera lenses on his CCD?

Peter...

[Merlin66]

I got a x2 convertor body for my ol' Zuiko lens and added a 1.25" sleeve.

This now allows me to used any Zuiko lens with the ATiK cameras.

(I've set up a 135mm +ATik16ic as an electronic finder....)

[swag72]

Cheers Ken and Peter. TJ's pictures look very good.

Anyone have any other ideas? Would really welcome some more thoughts.

[angusb1]

I think it comes down to a tradeoff between price and convenience. To use your existing lenses is cheap relative to buying refractors and possibly focal reducers to give you the same choices of focal lengths, and you may already have some good quality glass, but there will be issues from going down that route:

1 Guiding.

2 Focusing with lenses is more tricky as you have to make very fine adjustments.

3 Filters can only be changed by removing the adaptor from the lens, this will mean taking a lot of flats.

The geoptik adaptor is 19mm thick, if you use an Atik 314l+ the distance between sensor and the front of the camera is 12mm so this leaves 13mm spare if you are using Canon EF lenses with a flange focal distance of 44mm. You could fit the TS off axis guider in this distance but it would need to go in front of the camera and behind the adaptor which means the 1.25" filter would be in front of the prism in the guider. The upshot of this is that there would be a small clear aperture which would be dimmer than normal because of the filter in front, so it might be difficult to find a guide star. This effectively means that you can't have both OAG and filter so you would need to guide using a side by side bar or piggyback mount a guider on top of the lens/adaptor. The adaptor does have a bracket available to fit a finder scope to it so you could use a finder guider.

Unfortunately there aren't any filter wheels or drawers (that I know of) which have a depth of 13mm or less.

The only way I can see of being able to use an EF lens and either a filter drawer or an OAG is to use this EF adaptor from Telescope service (14.5mm) and this filter drawer (15mm). I started a thread about this EF adaptor to see if anyone has used it but no-one has responded so it's a bit of an unknown factor. The geoptik one is tried and tested so we know it's sturdy enough, the TS one may have flexure which could cause problems.

If you went down this route you would have still to use a side by side bar for guiding, and the lens would have to be mounted to the bar using a tripod foot.

The alternative is to spend more but use refractors which would give you the focal lengths you want for your targets. Since you plan to use a small chip ccd you can use a focal reducer to vary the focal length of any refractor. This will result in brighter images (lower F number) so shorter subs and less impact from guiding errors, but you should probably consider flattener/reducers rather than just reducers when you look at which refractor to buy.

This route is tried and tested, focusing is much more straighforward, you can use a filter wheel, and you can buy tube rings off the shelf allowing the attachment of finder guider or guide scope to eliminate differential flexure in guiding.

Its not a straightforward choice, the convenience of using an apo refractor and reducer/flattener is not cheap, and there is the allure of the prospect of having so many focal lengths available if you use your lenses. I have no experience of using refractors for imaging so I'm afraid I can't offer any useful help there but there is a wealth of information available, your starting point should probably be working out what targets you want to image. This will enable you to try and find the right focal length apo refractor and reducer/flattener to compare to your lenses.

Hope this helps

[swag72]

Thanks for the very considered reply Angus. I think prior to last night I was totally up for the Geoptik, but since trying to focus the 1000D and the camera lens, I can't help but think that it was a total nightmare and took me in excess of 2 hours to get it right. So I'm now erring towards the small Borg. If I want a widefield I can always stick the DSLR on it.

The thought of being able to use the filters is very appealing (even if I've not tried it yet!!)

Oh well, I may have a look at the mini Borg when I pop back to UK next week and see what I think.

[Psychobilly]

What a waste of those lovely L's.... focusing is a lot easier with the TS adaptor ( I made my own) ... Remember the L's were designed to give coverage on full frame sensors so you'll be nicely in the sweet spot with a small ccd....

Focusing a canon lens on the 1000D = Did your try remote manual focus from Eos util .. this allows you to make very fine focus adjustments without touching the lens... you can even get FWHM based AF using APT...

You use liveview - zoomed as well if you like and then the button under the focusing <<< <<< < > >> >>> oo for coarse,medium and fine adjustment and infinty...

Peter...

[angusb1]

Oh well, I may have a look at the mini Borg when I pop back to UK next week and see what I think.

I think this would be a good idea, having made a lot of decisions in the past without seeing all the options, I think having a good look at the mini Borg would enable you to make an informed decision.

focusing is a lot easier with the TS adaptor

This is worth bearing in mind. Peter is speaking from first hand experience, no substitute for that.

[swag72]

Don't worry Peter, those lovely L's will still get use!

The focus though really WAS very tricky indeed. If I go down the adaptor route I will definitely get that TS adaptor - Everything helps!

I have written out my steps for tonight, looking nice and clear, so I'll give it another go!

[Psychobilly]

Don't get me wrong the Borgs (apart from an almost incomprehensible parts list when your tryign to work out what you need to order to get everything working...) They are superb optically...

But ask Olly what he thinks of the Canon 200mm f2.8L with the focus adaptor...

I know waht a paing focusign lenses onthe DSLR can be... But since I discovered remote focusing of the lenses I haven't used the adaptor... but if I ever use the lenses on another CCD then it will be coming out to play again...

If your out tonight give it a whirl

[swag72]

I've spoken to Olly about this already. He hasn't helped . I think that I will try remote focusing tonight - Didn't even know it was on EosUtilities!

I'll see how I go between now and when I go back to UK on Tuesday. Have a look at the Borg and run from there - Then hide the bill from hubby!!!

[Psychobilly]

Full Remote manual focusigng isn't available on the 1000D I just dug out the 1000D and checked... however manually assisted autofocusing through liveview is...

With the later bodies you can focus the L lenses remotely (at least the ones I have tried) even when the focus mode is set to manual...

Peter...

[swag72]

Cheers Peter, I was just going to ask you about that as I'm all set up and fiddling and it wasn't an option open to me.

[Psychobilly]

I'll do a couple of screen grabs...

On the 1000D leave the lens in AF mode

Select Remote live view shooting on the camera control panel

Drag the white box over the area of interest and coarse focus <<< << and >> >> then zoom in and fine focus < > ... on a stellar target hit the infinty symbol to quickly set the lens to "infinty" focus and tweak from there

BIAB