EP projection

[erialc79]

Hello Folks,

Please could someone tell me about EP projection and Prime focus. Have just bought a modded Vesta and have been reading up on imaging and came across these phrases?

Currently using a Skywatcher Skyhawk 114 with a 1.5 Barlow and imaging saturn. Have managed to sharpen my pics by stacking more data, but dont have much detail - no bands

[Talitha]

Eyepiece projection is what they call it when you take images through a scope using an eyepiece for magnfication. Prime focus is when you remove the eyepiece and attach the camera directly to the scope, with no eyepiece involved. The scope is basically a high powered lens for the camera during prime focus astrophotography.

[legion48]

Further to Talitha's reply, EP projection will give you a significantly larger image scale, as show below:

x4 barlow

EP projection (9mm ep)

[barkis]

I think most planetary imaging is done using a webcam and a Televue Imagemate. They come in various amplifications from x2 up to x5. A lot will depend on what your scopes f ratio is.

A ratio of f20 is good. If you wanted to reach that figure, and your scope is f5 say, then a x4 Imagemate would be needed.

Bear in mind, these devices are not cheap though.

They do crop up secondhand now and again though.

Ron.

[The Warthog]

If one were interested in doing old fashioned ep projection, where would he get the bits and pieces for it?

[Kokatha man]

If one were interested in doing old fashioned ep projection, where would he get the bits and pieces for it?

Every now and then I hanker for a bit of "retro" exercising W, even though I use TeleVue barlows (2x & 3x) and a 5X Powermate and various extension tubes to up the scale of each.....

To this end I've removed the "end" of a GSO extenion tube (2", 80mm) and lathed a shallow groove in the (now) cut-off end resulting in a 2" barrell approximately 60mm long with a brass compression ring clamp in each of its ends.....the upper end takes a standard 50mm GSO extension tube to which the dslr T-piece can fit into and the other end a 2" to 1&1/4" reducer which has the eyepiece fitted to it such that the eyepiece is inside the barrell of the modified tube.....and of course I can put another reducer in the top end to use the DBK21 instead of a dslr....!

I wanted to see how the old EP projection stacked up against the 5X Powermate and DBK21 but haven't had the time (or weather!) as yet.....if you're interested I could post some pikkies that'd make understanding it much simpler - this arrangement also allows one to shift the distance from the ep to whatever camera sensor you use to vary scale as per the TeleVue website info....!:D

[legion48]

If one were interested in doing old fashioned ep projection, where would he get the bits and pieces for it?

This is what I use to attach the Toucam to the eyepiece:

£25.00 from Astro-Engineering - follow this link Adaptors for telescopes

[Macavity]

Very easy with Baader Hyperions - they have an screw adaptor... for almost everything.

Personally (And notwithstanding possible disadvantages) I found the technique far easier than reconfiguring / messing around with extension tubes, barlows etc. With no extra distance added, the 24mm Hyperion gives about the same image scale as prime focus. Of course, with additional extensions, or a shorter focal length e.p. you can get huge(!) magnification. The Vignetting seems to be less, and focussing seems to "snap in" rather better too... Well worthy of a go, I reckon, though.

[brianb]

If one were interested in doing old fashioned ep projection, where would he get the bits and pieces for it?

For a Newtonian there is a problem because of lack of inward focus, but there is a device widely available which consists of a T threaded tube into which a (small) eyepiece can be fitted, this has a 1.25" nosepiece. It's a versatile bit of kit because the nosepiece can be unscrewed and used, threaded onto the T mount as used for prime focus imaging, and (with no EP inside) the tube can be used as a T mount extension tube, should you need such a thing.

EP projection works well for high magnifications, higher than most people really need though x4 or more is really needed with short focus scopes. Because the output from the EP is designed to be parallel, not converging, significant aberrations are likely if using magnifications much smaller than about x4. In film days I used to use a 12mm EP for eyepiece projection giving a magnification of about x6 with what was considered then to be reasonable results.

[The Warthog]

Thanks, guys, I'll have a look round and a think.