Eyepiece projection

[nigel999]

Dear all,

Reading up on Baader hyperion eyepieces : Here:

First Light Optics - Baader Planetarium

I see that adapters can be obtained for these eyepieces to connect to a camera T mount. I see that Vixen seem offer similar (albeit far more expensively)

In this, are we looking at what birdwatchers with their spotter scopes refer to as "digiscoping" , or something similar?

If so, this seems remarkably simple... perhaps, to good to be true.

To be honest, the method sounds good perhaps (seeing what birdwatchers do) for terrestial work, but nobody seems to mention it for astro imaging.

So, what are the probs with "eyepiece projection" ..is it focusing , or a number of things?

Cheers, Nigel

P/S I would be using a DSLR (Nikon)

[nigel999]

Has nobody any comments observations or experience of eyepiece projection?

Cheers, Nigel

[jgs001]

Nigel, I've tried it, I think that not many people do actually do it which is why no replies. Focussing is hard, and the effect is like using barlows to increase magnification. You get a 'slower' optical system leading to longer exposure times. Even in the moon. Add all that extra glass to the mix, and you run the risk of degradation to the image quality. Does it work, yes. Given the cost of the adapter if you already have the ep's is it worth a try, probably. You may have more success than I did, or more patience.

[JB80]

When I first got my adapters I tried it on the moon with depressing results, so much so I decided to do away with that side until later on. But seeing as you have mentioned the Hyperion's I have just got myself a zoom with the thread. I have only had it a week but used it twice with my PST and it seems to get results of sorts, chase up a couple of threads by 'Photosbykev' in the solar imaging forum to see what he is managing to do with it.

I haven't tried it on the moon yet but I fully intend too I suspect the results will be better than my first attempts.

Still as John mentioned there are many reasons that it is not more widely used, I'm sure it can be made to work it's just a harder way to go about it.

[MikeD]

I use EP projection with my 10" newt and dmk21, I usually use the 10mm ep that came with the skywatcher newt.

Works well for me.

Mike.

[Macavity]

Works well for me.

Indeed. (Wow!)

Some eyepieces make the process rather simple - Especially Baader Hyperions. At least for Webcam use, all you need is a thread converter and a simple, inexpensive adaptor.

http://www.alpineastro.com/Hyperion-Eyepieces_com/Images_and_Docs/Hyperion_Manual_2.pdf

Aside: With no additional extension, the Hyperion 24 gives me about the same image scale as the objective at prime focus. Eyepiece projection can then access "high magnifications", via change of eyepiece or adding (post-eyepiece) extensions - But notably without major changes in the basic configuration?

[SJC03]

Hyperion`s for focal projection do work, I find the GSO 8" F4 astrograph I have and a Canon 40D work very well with a 17 Hyperion on the Moon. However I do not have good results with my 80mm Zenithstar refractor.. infocus and light gathering seem to be as mentioned a problem. I do like Hyperions though for viewing and have 8, 13, & 17 eyepieces. The thing is if you get a result it does give you what you see of the view which a normal telescope/camera focal projection will not.

[Moonshane]

I once used a 120mm achro refractor and 18mm Radian and the zoom feature on the camera/manual tracking to get these images with a point and press scope (Nikon Coolpix 995).

[nigel999]

Very interesting, thanks everyone, Some interesting images to boot!

It seems then I have little to lose by having a go at it. The Baader adapters are only £9 or so....and the hyperions seem good ep's. So buying at least on of the range will do no harm.

I must say though, my initial primary use for EP projection would be terrestial subjects, so perhaps light may not be such an issue.

Incidentally, when a DSLR is directly coupled to the scope (no ep or diagonal) how do you work out the magnification strength received?

I assume it involves the focal length of the scope but with no ep where does the rest of the formaula arrive from?

Cheers, Nigel

[jgs001]

Shane, they're pretty good, but that's afocal, rather than EP projection. EP projection removes the lens from the camera, and uses the eyepiece instead.

[Macavity]

Incidentally, when a DSLR is directly coupled to the scope (no ep or diagonal) how do you work out the magnification strength received? I assume it involves the focal length of the scope but with no ep where does the rest of the formaula arrive from?

In a similar way to the "accurate" method for eyepieces, where the field stop diameter is known

i.e. using (skool!) "trig" methods and small angle approximations.

But, since it's easier on my calculator (angles set to degrees!):

Field of View = INV TAN (chip dimension / scope focal length)

Thus a 10mm (Ahem "1/2 inch") chip in a f = 500mm scope will display an object of size:

INV TAN (10/500) = 1.145 Deg. (i.e. Two and a bit lunar diameters!).

An APPROXIMATE rule of thumb, a "half inch chip" has about the same field (magnification, if you insist!)

as a 8-10mm eyepiece. A 35mm (SLR?) chip / photo frame about the same as a "Pan 35" or similar ilk.

[Moonshane]

Shane, they're pretty good, but that's afocal, rather than EP projection. EP projection removes the lens from the camera, and uses the eyepiece instead.

oops sorry guys - told you I was no imager!

[nigel999]

In a similar way to the "accurate" method for eyepieces, where the field stop diameter is known

i.e. using (skool!) "trig" methods and small angle approximations.

But, since it's easier on my calculator (angles set to degrees!):

Field of View = INV TAN (chip dimension / scope focal length)

Thus a 10mm (Ahem "1/2 inch") chip in a f = 500mm scope will display an object of size:

INV TAN (10/500) = 1.145 Deg. (i.e. Two and a bit lunar diameters!).

An APPROXIMATE rule of thumb, a "half inch chip" has about the same field (magnification, if you insist!)

as a 8-10mm eyepiece. A 35mm (SLR?) chip / photo frame about the same as a "Pan 35" or similar ilk.

Oh lor Showing my ignorance now...cannot recall covering "inv tan" in school maths....mind you it is a horrendously long time ago.

So, using that, what sort of mag could I expect from a scope with focal lengths of 500, 600 and 700 mill respectively.

Using a camera with a sensor size of 23.1 mill by 15.4 ?

Obviously, I'm after figures which will give me a rough approximation of mag for whatever scope I end up with. Must admit, I really don't relate to metric, it's easier to calculate in it (if you have the skills ) but I cannot imagine things in metric..600 mill is near on 2 foot , always will be I think

Cheers, Nigel

[Macavity]

How about one worked example, and the rest as an exercise for the reader.

For a 600m scope:

INV TAN (23.1/600) = 2.2 Deg

INV TAN (15.4/600) = 1.5 Deg

Seriously though, Chip "size" can be a rather nebulous(!), so the values not THAT accurate.

Add or subtract 20% for the other focal lengths AND allow for variations of the theory?

Aside: I once bought, quite an expensive eyepiece, with a view to "neatly framing" the full moon.

In short, it didn't - By quite a large (negative!) margin.