Geoptik to Camera Lens Adapter

[Shelster1973]

Was wondering if someone could help me out with a very quick question.

As I am now loving and using my Star Adventurer Mount am wanting to be able to put my CCD onto the Nikon glass I have and have been looking at the Geoptik adapter but am a bit concerned / confused over the ability to use filters with it as the blurb says that the ability to screw in 1.25" and 2" filters is only on the Canon model.

Is this true?  Seems a bit strange as to why it is only available on the Canon one.  If there is a good technical reason, can someone explain for me?

Do not want to go down the road of buying Canon glass just to be able to use my CCD and filters with it all.

Suppose I could look at putting the filter wheel in there as it is, but not sure if I getting close to weight limits and also if I would be able to get sufficient backfocus on there too

[davew]

They accept 1.25" filters and not 2". 

http://www.geoptik.com/index.php?route=product/product&path=93&product_id=126

Reason is different throat size as far as I'm aware. 

Dave.

[zicklurky]

Yeah looks like the Canon version accepts 1.25" and 2" filters, but the Nikon version only accepts 1.25"

[Shelster1973]

Cheers for the update Dave.

Could go for it and then need to look at getting 1.25" filters instead of the Canon glass.

Working out distances looks like I would need to get an 8 or 7mm extension tube in there to give the correct distance between lens flange and CCD chip (46.5mm - 21mm for Geoptik - 17.5mm for camera chip depth from front of unit - 1mm if I put a filter into the train)

[geordie85]

How about something like this? 

https://m.aliexpress.com/s/item/32809854517.html?spm=a2g0n.search-cache.0.0.2a56fff3ZnmYo6#autostay

[Shelster1973]

I think weighing up my options I will be going for the Canon one and then look at either getting a cheap second hand 50mm lens or possible the 40mm pancake

[Dave S]

This is a good one to consider at under £110.

https://www.jessops.com/p/canon/ef-50mm-f-1-8-stm-lens-96690

Dave...

[old_eyes]

On 10/14/2017 at 18:27, Dave S said:

This is a good one to consider at under £110.

https://www.jessops.com/p/canon/ef-50mm-f-1-8-stm-lens-96690

Dave...

The Canon 'nifty fifty' is a super lens for widefield imaging. Strongly recommended.

Edited October 16, 2017 by old_eyes

[Shelster1973]

Thinking of lenses...would one of these work on the Geoptik

I know nothing about Canon fits sorry.

[MartinB]

I have a Geoptic and couldn't fit a 2" filter with my Canon lens although I may be doing something stupid.  Almost fits but not quite.  However, Astronomic make T2 filters which fit nicely between camera and adaptor.  I have an Ha and CLS and they give me just enough back focus.  I have found the adaptor quiet awkward to use in practice, I don't think you could get away with a filter wheel so filter changing is a big issue, I have only used with OSC.  Also you can't rotate your camera so I use a geared head which makes things a bit more clumsy.  I suppose that's only the same as you would if using a DSLR

[Shelster1973]

Have decided to get one of these instead.

Will now get the adaptor and see how things go from there

[Shelster1973]

Adaptor on the way now 

1st numpty question...how do you go about changing the F number on that lens I have ordered?  I do not have a Canon camera, so cant be adjusted on there

[geordie85]

I'd imagine you'd have to borrow a canon as it's not a manual lens. I could be wrong though.

You could be cheeky and pop into a canon shop and ask to try out one of their cameras with your lens and change the f number then. But that all depends if they'll let you. 

[Shelster1973]

Ah...this could get interesting then.

I take it the lens maintains the F ratio you set when you take it off the camera then?

[Shelster1973]

Just remembered...I have a 400D that I bought ages ago to try out the astromod, but decided not to go for it as cold not control it fully from my computer, that is / was sat in the loft.  Just dug it out and now charging the battery up for it

[ollypenrice]

What about using it wide open and making a front aperture mask to stop it down? I did this to avoid diff spikes which are pretty intrusive on starry fields of view. 

 

 

 

 

[Shelster1973]

Aperture mask is a good idea. Am guessing does not cause any vignette issues?

[Alien 13]

1 minute ago, Shelster1973 said:

Aperture mask is a good idea. Am guessing does not cause any vignette issues?

It can do if you go to extremes but normally you step down to something like f/4 which often seems like the "sweet spot", a step down filter ring is often an easy solution, this is an example  https://www.ebay.co.uk/i/281824071625?chn=ps&dispItem=1&adgroupid=49523053841&rlsatarget=pla-352776031395&abcId=1128956&adtype=pla&merchantid=113698737&poi=&googleloc=1006867&device=c&campaignid=857339205&crdt=0

You would need to calculate the size required for your lens filter thread and required f/stop.

Alan

[RichLD]

On 19/10/2017 at 20:17, MartinB said:

I have a Geoptic and couldn't fit a 2" filter with my Canon lens

This could be due to the lens being an EF-S variant (for crop sensor only). They protrude further past the flange than EF lenses. You can't use the EF-S lenses on a FF camera because they foul the mirror. I have two of the Geoptik Canon adapters and have no issues using 2" filters with EF lenses.

HTH

Rich

[MartinB]

2 hours ago, RichLD said:

This could be due to the lens being an EF-S variant (for crop sensor only). They protrude further past the flange than EF lenses. You can't use the EF-S lenses on a FF camera because they foul the mirror. I have two of the Geoptik Canon adapters and have no issues using 2" filters with EF lenses.

HTH

Rich

I've been using EF, not EF-S.  I'm probably doing something stupid, as usual.

[geordie85]

Would this adapter take 36mm unmounted filters?

[Shelster1973]

and in another twisty turny development..... while looking at the FLO website over lunch, noticed one of these and was wondering if I would be able to use this to convert my Nikon glass into a Canon connector and then use that on the Geoptik.

Image train then as follows      Nikon Lens > ZWO Adaptor > Geoptik Adaptor (inc filter) > any tubes needed for back focus shenanigans > CCD

All I need to know now is how much that adds to the image train and then work out the correct spacing for a Nikon lens.

[Shelster1973]

Think I have it all sorted now.

Ordered an adaptor from Amazon that converts Nikon F mount to the Canon.

Arrived today, fitted it with the spacing that I had done to get the Canon lens to work and the spacing seems to be spot on.  The Nikon has a Flange Focal Distance of 46.5mm as opposed to the 44mm for the Canon.

Only issue is that the Nikon lenses default to max f-stop when not fitted, so have had to imagineer a bit of folded card that wedges between teh edge of the adaptor and lens that can be moved to manually alter the aperture blades.  Have adjusted by eye to what appears to be f-4, which I am basing on eyeballing it when I did a exposure preview.

Hopefully it is looking clear tonight, so am wanting to get out and try a bit of Ha action with my 50mm lens.

Did try last night with the Canon and was not hugely impressed.

Have attached a very quick jpeg conversion of one un-callibrated sub.  Seems to be inconsitnet focus across the image.  The lens was at f-1.8 as could not stop it down as my Canon I thought I could use is non functional.

[rorymultistorey]

On 30/10/2017 at 17:44, Shelster1973 said:

Think I have it all sorted now.

Ordered an adaptor from Amazon that converts Nikon F mount to the Canon.

Arrived today, fitted it with the spacing that I had done to get the Canon lens to work and the spacing seems to be spot on.  The Nikon has a Flange Focal Distance of 46.5mm as opposed to the 44mm for the Canon.

Only issue is that the Nikon lenses default to max f-stop when not fitted, so have had to imagineer a bit of folded card that wedges between teh edge of the adaptor and lens that can be moved to manually alter the aperture blades.  Have adjusted by eye to what appears to be f-4, which I am basing on eyeballing it when I did a exposure preview.

Hopefully it is looking clear tonight, so am wanting to get out and try a bit of Ha action with my 50mm lens.

Did try last night with the Canon and was not hugely impressed.

Have attached a very quick jpeg conversion of one un-callibrated sub.  Seems to be inconsitnet focus across the image.  The lens was at f-1.8 as could not stop it down as my Canon I thought I could use is non functional.

i've just come in from a night of imaging and had exactly the same thing...  Did you figure is out.  I'm guessing tilt either on my filter or the lens is dropping slighly in the adapter. 

[Shelster1973]

Sorry, I never got round to sorting this one out. Had a lot of other stuff going on that distracted me away from investigating any further.

i still reckon it is down to the lens being wide open and the issues that causes with focusing exactly. 

As I now have the opportunity, I will look back into this and see what I can do to resolve it.