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Old 19-01-2019, 01:42 AM
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Ukastronomer (Jeremy)
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Question for the DSLR imagers please

I am NOT an imager, unfortunately being Autistic I never will be as I don't have the necessary patience, but I am connecting my DSLR to my scopes.

Therefore I have the most basic problem you will all have overcome.

72mm ED Skywatcher and 120mm Triplet ED Esprit.

Can not focus on infinity, assuming not enough inward travel.

See images

I have tried attaching the camera directly to the scope (72mm) NO luck, attaching the camera via 2" diags to the larger scope, NO luck, the only way is to use a reducer? screwed into the front of the camera nosepiece

So, is that it


Thanks
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  #2  
Old 19-01-2019, 02:15 AM
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Ukastronomer (Jeremy)
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Oh, the SCT is fine just vignetting

(Oh forget the image, through dirty window, raining out)
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Old 19-01-2019, 09:06 AM
tim.anderson (Tim Anderson)
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Quote:
Originally Posted by Ukastronomer View Post
I am NOT an imager, unfortunately being Autistic I never will be as I don't have the necessary patience, but I am connecting my DSLR to my scopes.

Therefore I have the most basic problem you will all have overcome.

72mm ED Skywatcher and 120mm Triplet ED Esprit.

Can not focus on infinity, assuming not enough inward travel.

See images

I have tried attaching the camera directly to the scope (72mm) NO luck, attaching the camera via 2" diags to the larger scope, NO luck, the only way is to use a reducer? screwed into the front of the camera nosepiece

So, is that it


Thanks
I assume you can get focus using an eyepiece and diagonal. If that is the case, then you should be able to get focus on the DSLR sensor (since it is just a matter of placing the sensor at the same distance from the lens as your eye would be).

I recommend not fitting the diagonal when using the DSLR. It gives you no benefit, and causes some light loss. Instead, connect the DSLR+bayonet adaptor+nosepiece straight into the focusser drawtube. However, to achieve the required "out-focus" distance, you will almost certainly require one or more spacer rings attached in front of the nosepiece.

I use this setup and mostly require about 25mm worth of spacers to get the focal plane of the camera to the same distance from the lens as a diagonal+eyepiece uses. Use enough spacers to avoid having the focusser drawtube racked out close to its maximum travel (many focussers in the racked-out position will droop under the weight of the camera, causing parts of your picture to be out of focus).

Hope that helps
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Old 19-01-2019, 12:10 PM
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that_guy (Tony)
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The ED72 will not come to focus without an extension tube if you're not using the reducer/corrector. Probably the same with the Esprit since they're designed to be used in conjunction with these.
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Old 19-01-2019, 12:13 PM
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Camelopardalis (Dunk)
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Typically, a refractor will need a field flattener for a camera sensor the size of a DSLR. The deliberate bonus with that strategy is that flatteners are usually designed so that the back focus is around 55mm, which is the same as a camera T-adapter and DSLR.
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Old 19-01-2019, 02:23 PM
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Icearcher (Chris)
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Hi Jeremy

I added a 50mm extension to mine and this works a charm, you should be able to use shorter ones but this worked for me.

Pic attached to illustrate.

Regards
Chris
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Old 19-01-2019, 08:40 PM
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Ukastronomer (Jeremy)
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Thank you all for taking the time to reply.

So

You are saying I need to increase the distance between the camera and scope, thanks
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Old 22-01-2019, 11:59 AM
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sil (Steve)
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Quote:
Originally Posted by Ukastronomer View Post
Thank you all for taking the time to reply.

So

You are saying I need to increase the distance between the camera and scope, thanks
the question becomes "how much distance?"

for an estimate and confirmation this will solve your focus problem deteach the camera from the scope, focus the scope on something with eyepiece and (get a friend) open the shutter on the camera with no lens or anything attached and just hold it steady in position as if it was attached so you can see the target on the live view, move the camera forward as if winding in the focuser and repeat moving outwards. Observe the live view, is it getting sharper or blurrier whwen you moving closer to scope? if clearer and it touches the focuser without achieving focus your combination wont work. More likely it'll get cleaer as you move it back and try to hold it still at the point it seems perfectly focused and get friend to measure the gap between scope and camera mounts, thats about the size spacer you need to get.
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Old 22-01-2019, 08:39 PM
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Ukastronomer (Jeremy)
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Thanks
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Old 22-01-2019, 08:41 PM
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Ukastronomer (Jeremy)
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I do have this I could not remember what it was for 'till I asked here
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Old 23-01-2019, 12:38 PM
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As I mentioned earlier, with your Esprit at least you want to use the dedicated flattener to ensure round stars right across the field. This also makes the spacing child’s play because the Canon adaptor just threads on the back of the flattener.
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