C-ED80 Prime focus is an Extension tube needed

[Dr Dixon]

Guess the title say it all, i am thinking of getting a canon 40D/450D to image at prime focus on a Celestron ED-80, it has a T-Thread on the drawtube of the Rack and pinion focuser but question i have is does this require an externsion tube to get focus? if it does what is the recommended length?

cheers

Ian

[Psychobilly]

Yes Get something around 50mm... better to work with the focuser racked in with a longer extension tube...

Peter...

[astro_dt]

Hi Ian

I can't answer in regards of your specific scope but I got a standard set of M42 photographic extension rings for under £10 on ebay.

They came as three rings 11/22.5/32mm (I think) and can be used in any combinations.

I have found uses for them in multiple set ups and they are one of the most useful purchases I have made!

Cheers

Danny

[jgs001]

Yes you do. If you attach a camera to the T thread, it can't quite extend out far enough to achieve focus. a 50mm extension tube does the job very nicely indeed, and use the MaxDSLR adapter to fit that.

[Psychobilly]

Remeber M42 is not the same as T-Thread....close but no cigar... same diameter different pitch

[jgs001]

Oh. The 450d and C80ED is the exact combination I use.

[beamer3.6m]

Hi.

I use the 400d on the c80Ed and found it did not reach focus but to save money I just unscrewea the lens fron a Barlow lens and used the remaining part as an extension tube.

[astro_dt]

Remeber M42 is not the same as T-Thread....close but no cigar... same diameter different pitch

Good point! I never force the threads!

[Psychobilly]

But you don't get many threads going together ... I really wouldnt recommend it ....then again its not my camera hangign of there either....

If its a 1.25" barlow then your running the risk of vignetting you want the max possible celar aperture betwwen the scoep and the camera...

[jgs001]

This combo is what I use:

and they slot together into

I leave my 2" LP filter in the MaxDSLR adapter.

[Dr Dixon]

OK thanks for the advice,

So based on the above i can go for Standard 50mm T-Thread Extension tube £18 + T Ring £11.00.

Or

50mm 2 Inch Focus extender £17.00 + MaxDSLR Adaptor for EOS £25.00

Difference being that in the second option i assume the wider 2 inch fitting means that theres less chance of getting vignetting.

[arad85]

OK thanks for the advice,

So based on the above i can go for Standard 50mm T-Thread Extension tube £18 + T Ring £11.00.

Or

50mm 2 Inch Focus extender £17.00 + MaxDSLR Adaptor for EOS £25.00

Difference being that in the second option i assume the wider 2 inch fitting means that theres less chance of getting vignetting.

Think you've got it in one there Given the price of the camera/mount/scope you're going to hook up to it, I think it a bit short sighted to try and save £13 here....

[jgs001]

That's correct. As far as I can see, the vignetting with my setup is really small, yes it's a bit more expensive.

[Dr Dixon]

Thanks for all the advice

Went with the Max DSLR adapter and 2 inch 50mm extension tube, which hopefully will arrive soon just as all this cloud disappears (fingers crossed!)

In the end i bought a second hand Canon 40D from Ebay (Nice suprise was that when i checked it had only registered 900 shutter actuations!) which will double up as terrrestrial and astro camera.

Initially will look at shortish unguided exposures before moving into the dark arts of autoguiding

Ian