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for lo mag - High qual EP? - or bino-viewer?


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hi folks

I love my SW 200p F5 (1000mm fl) - it doesn't give the same immersive view as my old binoculars - but it is less arm/neck ache :smiley:

having got set up for higher mags - I am now going for a lo-mag pan-view solution maybe around 20-25mm or higher if poss.....

choices to make - technically I should aim for a max exit pupil of 5mm (ish) - but I am not sure how critical this is

1. would a 30mm 82 degree be out of the question because of exit pupil? is exit pupil really a critical limit?

2. presenty I am thinking around 20-24mm - a 24mm 82 has the same 2 degree FOV as a 20mm 100 but I reckon the 82 would be more 'immersive' since there would be less head/eye swivelling and better eye relief - does this seem reasonable logic?

3. would a better option be a bino-viewer with a pair of less heavy perhaps less quailty EPs at around 24mm or so with lesser apparent FOV (say 68-70 ish) to keep the weight down?

I don't mind the head/eye swivelling for higher mag work - but the aim here is for a relaxed & detailed pan-view - (also to act as a super-finder)

thoughts/experience much appreciated

alan

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Alan I haven't a clue about the binos other than they require a bit of work to set up on a newt. A 30mm 82° eyepiece will produce a fabulous 2.5° tfov in your scope. I use a 31mm in my f5 newt (6mm ex

At 50, the average maximum dilated pupil diameter is 6.2 with a large spread. 6mm should be OK for the majority of viewers. I have used a 40mm in my F/6 scope, and that could be a bit washed out (exit

The problem with binoviewers for wider fields is that you need to spend a lot more money on the binoviewer to get one which can use more than the 23mm maximum field stop that is usable with a set of c

Alan

I haven't a clue about the binos other than they require a bit of work to set up on a newt. A 30mm 82° eyepiece will produce a fabulous 2.5° tfov in your scope. I use a 31mm in my f5 newt (6mm exit pupil) and it would be my choice if it were me. I think a 5mm exit pupil is quite conservative, especially if your skies are reasonably dark.

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Alan

I haven't a clue about the binos other than they require a bit of work to set up on a newt. A 30mm 82° eyepiece will produce a fabulous 2.5° tfov in your scope. I use a 31mm in my f5 newt (6mm exit pupil) and it would be my choice if it were me. I think a 5mm exit pupil is quite conservative, especially if your skies are reasonably dark.

thanks damo - that was more or less where I was heading - but previous forum advice about useable exit pupil made me pull my horns in a little - glad to hear it may not be such an issue - will await any bino advice before deciding

cheers

al

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At 50, the average maximum dilated pupil diameter is 6.2 with a large spread. 6mm should be OK for the majority of viewers. I have used a 40mm in my F/6 scope, and that could be a bit washed out (exit pupil 6.67mm, 5.76 deg FOV), but did provide good views. I now "limit" myself to a mere 5.3deg FOV with the Nagler 31 (exit pupil 5.17 mm). This I find works better in even mild LP (and 82 deg is more immersive than 69 deg). I would expect that a 31T5 would be OK in an F/5 Newtonian. I used a Nagler 26T5 in Olly's F/4.1 20" Dob, and it was brilliant (6.3mm exit pupil, and about 1deg FOV).

Binoviewers do not work with big Naglers and the like. Very few 2" binoviewers exist, and the diameter of the housing of the EPs must not exceed your inter-ocular distance (72mm for me, so I have some leeway),

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thanks michael - I am edging towards a single wide field EP - probably a 30mm 82 degree - rather than a 20mm 100 degree or 24mm 82 degree - aside from the wider AFOV - the longer eye relief and reduced 'eye waggling' may help towards more relaxed viewing

cheers

al

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The problem with binoviewers for wider fields is that you need to spend a lot more money on the binoviewer to get one which can use more than the 23mm maximum field stop that is usable with a set of chinese binoviewers or the cheaper Baader binoviewers. You would need to use Siebert supercharged binoviewers, Denkmeiers or the Baader mark Vs to use a 27mm field stop without vignetting and all of these are quite expensive. A 23mm field stop roughly equates to a 25mm 54degree plossl, a 20mm 68degree EP, or a 16mm 82degree EP. If you want a wide field the 30mm 82degree EP's TFOV will be huge in comparison to the binoviewer's unless you spend a lot on the binoviewer. Also the binoviewer will need a barlow or glass path corrector with the newt which will reduce the tfov even more. Wide views are lovely with a binoviewer but the 30mm Explore Scientific EP is a huge TFOV for a very good price.

For me the best wide view with my chinese binoviewer comes from the BST Explorer 18mm pair I have, and also from the 25mm BSTs which vignettte a bit but are still very comfortable. I do hanker after the lovely wide view I would get from a 30mm Explore Scientific 82 degree though. I think wide views are a bit like aperture fever, you always want a bit more.

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 I do hanker after the lovely wide view I would get from a 30mm Explore Scientific 82 degree though. I think wide views are a bit like aperture fever, you always want a bit more.

This is very true! I can only squeeze 1.6° from my 12" newt (while retaining a sensible exit pupil)and although its a decent swaythe of sky, I often wish I had more! The 30mm ES is a cracking ep by the way. I compared one recently with a 31 Nagler, and hard a real hard time seperating them at f5.

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At 50, the average maximum dilated pupil diameter is 6.2 with a large spread. 6mm should be OK for the majority of viewers. I have used a 40mm in my F/6 scope, and that could be a bit washed out (exit pupil 6.67mm, 5.76 deg FOV), but did provide good views. I now "limit" myself to a mere 5.3deg FOV with the Nagler 31 (exit pupil 5.17 mm). This I find works better in even mild LP (and 82 deg is more immersive than 69 deg). I would expect that a 31T5 would be OK in an F/5 Newtonian. I used a Nagler 26T5 in Olly's F/4.1 20" Dob, and it was brilliant (6.3mm exit pupil, and about 1deg FOV).

Binoviewers do not work with big Naglers and the like. Very few 2" binoviewers exist, and the diameter of the housing of the EPs must not exceed your inter-ocular distance (72mm for me, so I have some leeway),

I'd only like to add that in heavily light polluted skies, 5mm (5.2mm) exit pupil is probably a good maximum, in my own experience, it's even worse on a full Moon!

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I'd only like to add that in heavily light polluted skies, 5mm (5.2mm) exit pupil is probably a good maximum, in my own experience, it's even worse on a full Moon!

thanks Naemeth - yes agree this is a risk :shocked: - thanks for the heads-up

anyways the die is cast now - I will just have to see (or not)

actually I just had my exit dark adjusted pupil re-assessed - not totally accurate cos you need light to see the pupil - but my wifey reckons my pupil is deffo larger than a 6mm dia. hole in card held near the eye - and that's with a red light to illuminate the eye......

so maybe it'll be Ok - also the LP in my garden aint that bad when looking seawards

cheers

al

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thanks Naemeth - yes agree this is a risk :shocked: - thanks for the heads-up

anyways the die is cast now - I will just have to see (or not)

actually I just had my exit dark adjusted pupil re-assessed - not totally accurate cos you need light to see the pupil - but my wifey reckons my pupil is deffo larger than a 6mm dia. hole in card held near the eye - and that's with a red light to illuminate the eye......

so maybe it'll be Ok - also the LP in my garden aint that bad when looking seawards

cheers

al

It probably isn't that bad for you. The LP in my back yard is not only bad due to glare (from streetlights I can't block out), but it's because I'm only around 1.3, perhaps even about 1 mile out of the city centre (depends where you go).

Even if your pupils don't dilate that far, you shouldn't see much change, if any if the difference is small. If it's big enough, you will start to see a black ring of the secondary in the centre of the field.

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Fwiw I can get roughly 1.1 degrees fov in my binoviewer and 10" newt, I moved the primary mirror so now I don't need the 1.6x corrector or a Barlow. Once you have viewed the moon, Jupiter,m42, the double cluster in a pair of bv's, there is no going back.

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It probably isn't that bad for you. The LP in my back yard is not only bad due to glare (from streetlights I can't block out), but it's because I'm only around 1.3, perhaps even about 1 mile out of the city centre (depends where you go).

Even if your pupils don't dilate that far, you shouldn't see much change, if any if the difference is small. If it's big enough, you will start to see a black ring of the secondary in the centre of the field.

stop it mr N - you're frightening me now! :smiley:

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Fwiw I can get roughly 1.1 degrees fov in my binoviewer and 10" newt, I moved the primary mirror so now I don't need the 1.6x corrector or a Barlow. Once you have viewed the moon, Jupiter,m42, the double cluster in a pair of bv's, there is no going back.

yeah a BW is still on the shopping list - b'day in March!

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stop it mr N - you're frightening me now! :smiley:

Seriously, it's not going to be that bad. That kind of image can only really be seen when you're looking through your lowest power eyepiece during the day.

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It probably isn't that bad for you. The LP in my back yard is not only bad due to glare (from streetlights I can't block out), but it's because I'm only around 1.3, perhaps even about 1 mile out of the city centre (depends where you go).

Even if your pupils don't dilate that far, you shouldn't see much change, if any if the difference is small. If it's big enough, you will start to see a black ring of the secondary in the centre of the field.

If your pupils dilate to 5mm, and the exit pupil is 7mm, you lose about half the light. Equivalent to turning a 14" newt inot a 10" (if your pupils dilate to 6mm you have turned it into a 12"). Image quality might not suffer too much, but you are losing light.

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I had a 2", 42mm 70 degree ep when I had the 8" dob, which supposedly gave a 2.45 degree tfov, yet I couldn't fit m45 in the ep. I never could figure out why.

Strange, that. I could just squeeze the Pleiades (at least the main stars) into one FOV with the 40mm Paragon (1.34 deg FOV)

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I had a 2", 42mm 70 degree ep when I had the 8" dob, which supposedly gave a 2.45 degree tfov, yet I couldn't fit m45 in the ep. I never could figure out why.

Hmm.... for my Heritage I get a 2.08 degree field with my 26mm Plössl (I love the widefield views of this scope!) and can quite easily fit the whole thing in, it's probably around 1.3 degrees but I cannot be sure.

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