Magnification of image with DSLR

[malc-c]

I've only had my scope a couple of weeks and last Saturday was an opportunity to try some photography using the body of my Olympus E-500 connected to the focuser. I removed the lens and connected the T mount to the 2" focuser and got some really nice prime focus images of the moon. I then pointed the scope at Jupiter but I was luck if I got anything more than a dot in the viewfinder.

I tried using the 32mm projection eyepiece from the Revelation kit but then found I couldn't focus the image.... I tried removing that eyepiece and using a barlow lens but again I was running out of focus... I couldn't work out if it was a case of needing to move the camera further out or in, my gut feeling was that I needed some extension tubes to move the camera about another 3" out.

Can anyone give me some tips on getting more of the planet, be that Jupiter, Saturn or Mars in the frame when using a DSLR. I also have a NexImage but again the image is quite small. I know I need to play with the camera settings in the capture software to get more detail, but the size of Jupiter is still small as can be seen in the final image after processing in Regifix and Photoshop

[brianb]

You will need to be imaging at f/20 to f/30 to record all the detail the scope can resolve (in good conditions). Your scope is f/5 so you need 4x to 6x magnification, this can be obtained using a good barlow or tele-extender (Powermates are popular). A poor barlow will degrade the image as much as it magnifies it ...

[malc-c]

The Revelation kit came with a Barlow, but I couldn't focus the image, so I'll investigate the tele-extender option. Thanks

[malc-c]

I have the Revelation eyepiece kit which contains a 32mm "camera projector lens"

From one of the web sites

The 32mm eyepiece is not only a superb and comfortable low power model but incorporates a precision sliding barrel and male T thread for imaging. Simply unscrew the cap to reveal the standard T thread that accepts any standard T ring to allow superb eyepiece projection astro imaging with a digital SLR camera. In addition to these features the 32mm projection eyepiece has the widest true field of view possible in the 1.25" format

I took off the eye cap, connected the T adapter and camera and was able to place the end of the barrel against my LCD monitor and focus on the individual pixels that made up a character on the screen, so I'm guessing that this should focus on the image at prime focus and enlarge the image suitably ?

Anyone else used this eyepiece ??

[Merlin66]

Eyepiece projection can certaily be used to give an enlarged image on the camera CCD chip. Generally we find the performance with a good barlow (or Powermate) is superior.

[malc-c]

OK gonna show my ignorance here...

If I understand the purpose of the barlow it basically shifts the prime focal point of the image further up the focuser. If I simply connect the T adapter to a 1.25" camera adapter which is inserted into where the eyepiece would sit in the barlow, how to I then get the camera to focus on the image if that shifted focal point is before or after the CCD chip ? (hope that makes sense ?)

[Merlin66]

You've got the general theory correct. The distance the barlow sits from the CCD is fixed; the focal length of the barlow is fixed; the only variable left is the position of the barlow inside the prime focus of the scope....that's the position you need to find for your set up.

[malc-c]

You've got the general theory correct. The distance the barlow sits from the CCD is fixed; the focal length of the barlow is fixed; the only variable left is the position of the barlow inside the prime focus of the scope....that's the position you need to find for your set up.

Could that be the problem, in that this point is outside of the distance the focuser can travel ?? If so what's the best way to resolve this ?

[Merlin66]

Are you saying, that if you put an eyepiece in the barlow (say your 32mm) that you are unable to focus on the moon/ bright star??

[malc-c]

No - this is (as far as I know as I have yet to use a barlow for visual work) only when using the DSLR body. I was able to place the body of the camera direct to the focuser's 2" and get some decent moon images.

But with the same set up when trying to capture Jupiter it was just a dot. I know that my scope is limited for planetary work being an F5, but wanted to get more of Jupiters disk in the field of view, so started playing with barows and the 2" extension tubes that came with the 200P, but couln't get anything usable through out the focuser range.

Using the experiment example above where when using the 32mm eyepiece projection eyepiece and my computer monitor I can't get any text on the screen focused in the camera viewfinder when using a barlow lense pressed up against the screen.

[Merlin66]

You won't get any image that way from the barlow set-up it needs a converging beam...

Just set up the barlow with the 32mm eyepiece focus on the moon, then replace the eyepiece with the camera.....as i'm typing this I realise you'll use a DSLR; the back focus will add another 55mm to the barlow spacing and increase the magnification ie if you use a x2 barlow...with the 1.25" Thread/T2 camera adaptor +DSLR you'll probably get closer to x3...so your f5 system will be working at around f15...larger plate scale .....

[yoda]

I know that my scope is limited for planetary work being an F5, but wanted to get more of Jupiters disk in the field of view,

I think the lower the f number (say a f5) the better it is for DSO's and the higther the f number (say a f10) the better for the planets and moon when astrsphotography is concerned.

[malc-c]

You won't get any image that way from the barlow set-up it needs a converging beam...

Just set up the barlow with the 32mm eyepiece focus on the moon, then replace the eyepiece with the camera.....as i'm typing this I realise you'll use a DSLR; the back focus will add another 55mm to the barlow spacing and increase the magnification ie if you use a x2 barlow...with the 1.25" Thread/T2 camera adaptor +DSLR you'll probably get closer to x3...so your f5 system will be working at around f15...larger plate scale .....

Thanks for that.. I think I follow what you're saying. The bit that worries me is the comment you make about "back focus" of the DSLR.

I guess the best thing to do is set the scope up and try out various combination, just have to use something land based as there seems little chance of doing any astronomy given all this rain

[malc-c]

One further question, as I have a NexImage CCD, would this give me better results when used with a 2x barlow, in terms of image size on the CCD. The Olympus E-500 is an 8MP

[Merlin66]

The plate scale/image size will be similar.... it will just fill up more of the smaller chip!