TheSkySearchers

Hi all new to the forum and looking for some information. I'm currently looking into buying some binoculars to start the hobby. My question is I've read that the average human eye has an entrance pupil of 7mm dependant on age when dark adapted and is best to buy some binoculars with an exit pupil lower than the 7mm stated above. Now I've been looking into acquiring some 10x50 bino's to get started with which as you will all know equal to an exit pupil of 5mm and wondered why the option to buy say 15x70 is available as this equals to an exit pupil of 4.6mm wouldn't the view you get be darkened on the 15x70's compared to that of the 10x50's and therefore a poorer option to choose? Now I know many people buy larger magnification binoculars but was wondering why so based on the information I have given above and what the advantages and disadvantages were of choosing one or the other? Thanks

1. Welcome aboard, Yshire!
2. You won't get a brighter image in 15x70 (vs. 10x50) binoculars, but you will get more magnification.
Both brightness and magnification are useful. For example, the moon is very bright. So if want to look at the moon, and you want to see more details on it, the 15x70 would be better. Note that at 15x, you would want to use a tripod for more stability. But the 10x50 will be lighter in weight, provide a wider field of view, and can potentially be used without a tripod, all of which are better for general stargazing. I'm just a novice on these things; I'm sure others here will have more to add.

Exit pupil vs aperture topic

viewtopic.php?f=49&t=5935

Welcome to TSS Yshire! There are many factors (magnification, aperture, exit pupil, contrast, sky conditions) determining what you will be able to see with binoculars or telescope. Selecting just by single parameter like exit pupil is not the right way to do it.

To make it simple larger aperture binoculars will show you more targets and more details in targets than smaller ones. The trade off is that larger binoculars are heavy and require use of mount and also have narrower field of view.

Most of us end up having a few binoculars of different sizes. The choice will depend on your observing style. For handhold observing you would want smaller binos 8x40 or 10x50. Some people with practice can do 15x70 handhold. However, majority would prefer to stabilize even 10x50 using a monopod or other simple means. Depending on the model from 10x50 to 20x80 one can get away with rather simple monpod/tripod setup. More expensive heavier models from 20x80 and up would require heavy duty mounts.

Another thing to consider is that when you go up in magnification proper collimation becomes more important. Many of us had good experience with inexpensive binos in 8x40 and 10x50 range. Starting from 15x70 you either would want to learn how to collimate them yourself or buy better quality model which come properly collimated.

I have a 10x50 Redmond that is all purpose, even for the night sky. For more serious use, I have 20x80 Oberwerks, but you need support for them as they are not made for holding. A parallelogram and surveyors tripod take care of that. If you want to get really serious, a 45°/100 should fit the bill.

Thank you all for your replies. The information is a big help. As some have mentioned with higher magnification weight increases so would anyone suggest instead of getting say 15x70 binoculars to learn the night sky would maybe a 70mm refractor on an alt-az mount be another option to choose from?

Yshire wrote: ↑Sun Jan 12, 2020 5:14 pm Thank you all for your replies. The information is a big help. As some have mentioned with higher magnification weight increases so would anyone suggest instead of getting say 15x70 binoculars to learn the night sky would maybe a 70mm refractor on an alt-az mount be another option to choose from?

I think 70mm will be somewhat limiting, but 80 to 100mm refractors on AltAz are lightweight and capable setup.

Saying that you can manage 15x70 binos on a simple monopod.

Bigzmey wrote: ↑Sun Jan 12, 2020 5:57 pm

Yshire wrote: ↑Sun Jan 12, 2020 5:14 pm Thank you all for your replies. The information is a big help. As some have mentioned with higher magnification weight increases so would anyone suggest instead of getting say 15x70 binoculars to learn the night sky would maybe a 70mm refractor on an alt-az mount be another option to choose from?

I think 70mm will be somewhat limiting, but 80 to 100mm refractors on AltAz are lightweight and capable setup.

Saying that you can manage 15x70 binos on a simple monopod.

Thank you my main concern with binoculars is viewing the zenith I know this can be helped with either a lounge chair or a parellelogram but the latter are quite expensive. Whereas I can only assume a monopod would only help with horizon viewing?

Yshire wrote: ↑Sun Jan 12, 2020 6:09 pm

Bigzmey wrote: ↑Sun Jan 12, 2020 5:57 pm

Yshire wrote: ↑Sun Jan 12, 2020 5:14 pm Thank you all for your replies. The information is a big help. As some have mentioned with higher magnification weight increases so would anyone suggest instead of getting say 15x70 binoculars to learn the night sky would maybe a 70mm refractor on an alt-az mount be another option to choose from?

I think 70mm will be somewhat limiting, but 80 to 100mm refractors on AltAz are lightweight and capable setup.

Saying that you can manage 15x70 binos on a simple monopod.

Thank you my main concern with binoculars is viewing the zenith I know this can be helped with either a lounge chair or a parellelogram but the latter are quite expensive. Whereas I can only assume a monopod would only help with horizon viewing?

Yes, lounge chair is required to observe high up with binos. I adjust the height of monopod to accommodate sitting or reclining position, and rest the monopod on the chair.

Your original question dealt with 7mm exit pupils. That assumes youth, non-smokers, and dark skies. We older folks are around 5mm. Most here recommend something like 10x50. A good choice if you can hold 10x steady enough. If not, get a mound. For hand holding, I prefer 8x56 for steadier holding. Otherwise, I love my 151x70s for quick evenings. For everything else, serious time, I pull out the 100mm. Anything around a 4-5mm exit pupil will give better magnification, and darker background so that objects show up better. Bigger aperture allows more resolving power, better detail. This is really evident on star clusters!

I also recommend a tripod or monopod for anything over 10x50. Or, like I do with my 15x70's you can lay down in a lounge chair and prop your arms on the armrests to keep them from getting tired. For my 25x100's I bought a dedicated mount from Oberwerk.