lowest power 2" ep for a 6" 1800mm mak

[Bender]

While I am waiting for my 6" 1800mm intes mak to arrive I was wondering if someone could help me to find out whats the lowest power 2" ep I could practical use.

Panoptic 41mm, 35mm or 27mm ?

Then there would be of course the question if the 2" eps could be to heavy.

[Doc]

Just in case you didn't know in this scope

41 Panoptic gives x44 mag, 1.55° FOV and 3.42mm exit pupil

35 Panoptic gives x51 mag, 1.32° FOV and 2.92mm exit pupil

27 Panoptic gives x67 mag, 1.02° FOV and 2.25mm exit pupil

[Bender]

Thanks Doc. I am curious if the mak can give me the 1.55 FOV. Is there a way to calculate this from the specs of he scope? Or do i have to now some internal baffling diameters from the scope?

[GazOC]

Having owned the 5" and 7" versions of the Skywatcher Mak I don't you will get much more than a 1 deg field with any eyepiece because of the size of the rear opening on the scope.

[Doc]

These figures are just from a magnification calculator I use and are not just for MAK telescopes, I forgot that Mak's have a smaller rear opening similar to an SCT.

With a SCT you can buy a larger visual back to enable you to get the full FOV possible, maybe a MAK has something similar.

[Macavity]

Unfortunately therein we come up against a certain amount of experiment... and FAITH even? It will [probably] depend on the potential for vignetting re. optical path (the hole though the mirror!) internal baffling etc. of the specific scope. If the scope can completely illuminate the field stop of these specific 2" eyepieces, all well and good. Sometimes even the theory can leave uncertainty - To both the advantage and disadvantage of the field. Perhaps best to borrow a Pan [whatever] of buy a cheaper 2", 30-something mm, 70 deg eyepiece for test purposes?

[Bender]

I got the Intes today , After i took the 1.25" diagonal of (unfortunatly i dont have a 2" so i cant just simply test my 2" ep, and i would like to avoid to buy one if it wouldnt make a difference)

I look at the hole for the light pretty much the diameter of the barrel of a 1.25" ep.

I guess that means there is not point buying a 2" diagonal as this hole would be the limiting factor?

[Macavity]

I look at the hole for the light pretty much the diameter of the barrel of a 1.25" ep.

I guess that means there is not point buying a 2" diagonal as this hole would be the limiting factor?

Maybe, maybe not.

** Since it's (hopefully) nice and bright outside, you could try poking the scope through some curtains, removing the present diagonal and focussing the image of the terrestrial scene onto a screen. Tracing (or grease-proof) paper is a good poor-man's ground glass screen.

This should give you a handle on the size of circle the scope is capable of illuminating in the field plane. Maybe even some indication of edge darkening, from vignetting. If there is a usefully illuminated circle of diameter greater than the canonical limit for 1.25" eyepiece (28mm or so?), it should be possible to use a 2" eyepiece... at some level.

The "worth it" factor is always a harder (individual) thing?

** P.S. Hopefully the neighbours won't call the cops!

[John]

...** P.S. Hopefully the neighbours won't call the cops!

"Well Officer, I was just tracing the size of my exit pupil on this grease-proof paper ....... no, I had no idea that the scope was pointing at Mrs Figgis's bedroom window ........ oh ? ..... well, I'm sure I can tell you the full details down at the Station .......

[david o]

I use 2" wide-field EPs in the Skymax 180 Mak (fL 2700mm @ f/15), hanging an SCT-Mak adaptor and a 2" SCT diagonal off the back.

The primary mirror baffle tube, where it comes through the visual back, has less than an inch of internal diameter.

But both my Series 4000 QX 30mm (70º aFOV) and Revelation SV 42mm (65º) are tack sharp right to the edge and show no vignetting.

Unfortunately the 55mm TV Plössl does. Badly.

I suspect that the Pan 41mm would be fine in your Intes.

HTH

[Bender]

Finally got around to test the exiting light circle diameter. (Used the living room lamp to avoid complains from the neighbours )

Found it difficult to get a nice and sharp circle but when i managed it looked like 1.5 inch. So definitely more than 1.25" but i guess not enough to illuminate a 41mm pan?

Maybe i just stick with my 26mm Nagler as low mag ep both for the dob and the mak.

[Macavity]

I suspect I was decidedly unclear re. the circle measurement thing? For what it's worth, it's important e.g. the (distant!) scene be focused on the screen. I used to focus the 'scope normally, then remove eyepiece and diagonal. The focussed image is found a couple (few) inches behind the OTA - Corresponding to the optical path length of the diagonal etc. That said, and for all the above meanderings, a full-field exploiting 1.25" eyepiece has (subjectively) not much less true field than yer typical (e.g. 32mm 70deg) 2" eyepiece.