Problem getting my Canon 5D MkIII to focus.

[SlimPaling]

Hi ... I hope that I am in the correct section to ask for help with my problem!

 

Can anybody help at all with my focusing problem???

Maybe somebody with a similar set-up to mine will be able to help??

 

At long last, after many delays, I am trying to embark upon Astro imaging using my Canon 5D MkIII on my APM 123/738 refractor.

I am attaching an image showing my current set-up.

 

I understand that the back focus for the flattener is 92mm and the back focus for my Canon 5D MkIII DSLR is 44mm .... this leaves 48mm in the focusing train which I have taken up with my EOS adaptor + 20mm M48 extension tube + a Variable M48 extension tube. and this distance has been set up very accurately using my vernier callipers.

 

Last night I discovered that I am unable to achieve focus because my focuser will not go forward (ie: inwards) enough as it hits the stop. At a very rough guess I need it to go in at least 5mm (or more) to get my Canon DSLR into focus.

 

Does anybody have any suggestions what I need to do here to be able to use my DSLR ???

 

Mike

 

[michael8554]

Hi Mike

You have the Flattener to EOS distance spot on, so all you can change is the length of the Riser.

An engineering shop should be able to make you a shorter Riser.

Alternatively, it would be a shame to hack such a beautiful (and expensive) riser, but the engineering shop may be able to shorten the Flattener end of your riser and cut a new male thread.

Finally, you might be able to cut off 5mm of the female focuser end of the Riser and still have enough thread to attach to the focuser - that will give you 5mm more in-focus movement before the new end of the riser hits the body of the focuser.

Michael

[Guest]

Hi Mike,

 

My setup is, APM LZOS 115/805 with FT 3.5 Focuser, and to save space and to avoid issues like you have, I did buy the adapter (see picture below) which saves a lots of space and I do not use any RISER ( though I have one RISER ).. see how I did attach the RICCARDI REDUCER to the FT3.5 without any RISER..

Maybe a possible solution for you ?  my REDUCER is the BIG ONE (M82) and not the small one (M63)

 

Cheers

 

Martin 

 

 

[SlimPaling]

Hi Martin ....

Thanks for this .... I have the same adaptor available as yours.

I have now removed my 4" riser and fitted my flattener using the same adaptor as yours .... I am now waiting for a suitable clear night to test things out. The long term weather forecast doesn't look good here in UK!!!

I actually made contact with APM about this and they have assured me that I don't need the 4" riser .... which is encouraging.

Also ... I have been in contact with Starlight Instruments (who make the 3.5" focuser and my 4" riser) ... and he told me the same thing ... "take off the riser and all should be well". He also told me that they can also produce a shorter riser , as a special on-off, if I find out that I need one. Obviously this "one-off" riser will come at a premium price .... but if it solves the problem I will have to go for it.

I am not sure why the company that supplied my scope told me that I needed a 4" riser in the first place.

I will keep this thread informed of any developments.

Mike

[Guest]

Good Luck Mike,

 

It will work for you w/o the riser, since same combination works also for me, though I mostly do not use any EOS CAMERA but mainly a CCD ( STL 1100M or QHY 183C ).

But would ge great to get update if your end, and if w/o the riser your focussing issues are solved..

 

greetings from Vienna

 

Martin

 

[SlimPaling]

On ‎29‎/‎03‎/‎2017 at 13:00, artem said:

Good Luck Mike,

 

It will work for you w/o the riser, since same combination works also for me, though I mostly do not use any EOS CAMERA but mainly a CCD ( STL 1100M or QHY 183C ).

But would ge great to get update if your end, and if w/o the riser your focussing issues are solved..

 

greetings from Vienna

 

Martin

 

Hi Martin ...

Last Friday I managed to test out my system as a fairly clear sky came along for a change!

My system worked perfectly without the 4" riser .... perfect focussing

I managed to get my first set of Moon images ... along with some deeper sky objects. The Moon images were pretty good but obviously I have a lot to learn about deep sky objects.

It is going to be a steep learning curve from now on ... but at least I now have a system that works !!!!

Mike

[Guest]

Thank you MIke for giving feedback, and happy that the new setup did work..

 

Regards

 

Martin