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magnification for terrestrial binoviewing?

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#1 ktss

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Posted 24 November 2022 - 03:00 AM

Hi folks, I have a sky-max 127 Mak (1500mm FL), with William Optics Binoviewer package, which includes 20mm 66 degree EPs. I wonder for the purpose of terrestrial viewing of landscapes, birds and wildlife in general, what is the highest magnification recommended? Is 10mm (150x) too much? Feels like during the daytime there's too much heat turbulence to see anything too far. 



#2 jprideaux

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Posted 24 November 2022 - 07:51 AM

Heat turbulence will be a real problem in general for using high magnification in daytime especially at distance. It is less of a problem when focusing at shorter distances. I use a fast refractor at very low magnification (around 30x) for my daytime use with binoviewers.
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#3 ktss

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Posted 24 November 2022 - 08:24 AM

I guess 75x is already quite high...



#4 Eddgie

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Posted 24 November 2022 - 09:25 AM

There are a great many variables.

 

If the subject is in a nearby tree where the scope is pointed up into the air, then you can use considerable power. It is possible to resolve details in the eyes and feathers.

 

In the early morning, very high powers are also possible. Long range shooters go to the range in the morning and use scopes to see bullet holes in targets at great distances.

 

On days with fresh snow, you can often use very high powers. The snow acts as a thermal blanket keeping heat from rising off of the ground.

 

All of that being said, as jprideaux says, heat is your major enemy to high powers along the ground, but the higher the subject is off the ground, the more power you can use.  A hawk in a tall tree 50 yards away might bear 60x. 

 

This is why so many birding scopes have 60x zooms.  The distances are generally no more than 100 yards and the birds tend to be up in trees.  



#5 DRodrigues

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Posted 24 November 2022 - 05:22 PM

If you want erected images the other problem (besides air turbulence...), for higher mags, is the poor quality of most image erectors - see http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%20image%20erectors

I do cr-binoviewing at >100x over wetlands with success - see http://www.pt-ducks....#CR-binoviewing 


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#6 ktss

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Posted 24 November 2022 - 11:29 PM

There are a great many variables.

 

If the subject is in a nearby tree where the scope is pointed up into the air, then you can use considerable power. It is possible to resolve details in the eyes and feathers.

 

In the early morning, very high powers are also possible. Long range shooters go to the range in the morning and use scopes to see bullet holes in targets at great distances.

 

On days with fresh snow, you can often use very high powers. The snow acts as a thermal blanket keeping heat from rising off of the ground.

 

All of that being said, as jprideaux says, heat is your major enemy to high powers along the ground, but the higher the subject is off the ground, the more power you can use.  A hawk in a tall tree 50 yards away might bear 60x. 

 

This is why so many birding scopes have 60x zooms.  The distances are generally no more than 100 yards and the birds tend to be up in trees.  

Thanks for sharing. Makes a lot of sense. I've not thought about so many different scenarios. 

Ok now I am going to buy two 3mm's. J. 


Edited by ktss, 24 November 2022 - 11:30 PM.


#7 ktss

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Posted 24 November 2022 - 11:32 PM

If you want erected images the other problem (besides air turbulence...), for higher mags, is the poor quality of most image erectors - see http://www.pt-ducks.com/cr-telescopes.htm#Test%20of%20image%20erectors

I do cr-binoviewing at >100x over wetlands with success - see http://www.pt-ducks....#CR-binoviewing

I've got a Long Perng 45 degree erecting image prism. I heard this one is not bad?



#8 Spartinix

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Posted 25 November 2022 - 07:19 AM

Thanks for sharing. Makes a lot of sense. I've not thought about so many different scenarios.
Ok now I am going to buy two 3mm's. J.

Two 3mm's... usually poor eye relief and if you've only used 20mm's with the bv you could be in for a real merging nightmare with 3mm's. Unless you know how to precisely align/collimate your bv, I'd get a 2x barlow (3-4x with bv), or a 4-5x telecentric for those 20mm's and be done with it.

Edited by Spartinix, 25 November 2022 - 07:22 AM.

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#9 ktss

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Posted 25 November 2022 - 07:49 AM

Two 3mm's... usually poor eye relief and if you've only used 20mm's with the bv you could be in for a real merging nightmare with 3mm's. Unless you know how to precisely align/collimate your bv, I'd get a 2x barlow (3-4x with bv), or a 4-5x telecentric for those 20mm's and be done with it.

3mm was meant to be a joke:)



#10 Spartinix

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Posted 25 November 2022 - 08:53 AM

Allright then :p

#11 DRodrigues

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Posted 25 November 2022 - 11:00 PM

I've got a Long Perng 45 degree erecting image prism. I heard this one is not bad?

Still never tested or read of any 45º erecting prism being good over 60x...



#12 ktss

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Posted 26 November 2022 - 08:13 AM

Still never tested or read of any 45º erecting prism being good over 60x...

Oh hell... didn't know 45 degree is this bad. How about 90 degree erecting prisms? Any good ones above 60x?



#13 DRodrigues

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Posted 26 November 2022 - 06:32 PM

Oh hell... didn't know 45 degree is this bad. How about 90 degree erecting prisms? Any good ones above 60x?

I never test it (not useful for my type of CR-birding...), but there is one 2" from Baader - not sure if is the Zeiss version but you can confirm it here at CN by searching for it.



#14 ktss

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Posted 26 November 2022 - 08:59 PM

I never test it (not useful for my type of CR-birding...), but there is one 2" from Baader - not sure if is the Zeiss version but you can confirm it here at CN by searching for it.

Thanks!



#15 luxo II

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Posted 27 November 2022 - 09:48 PM

Feels like during the daytime there's too much heat turbulence to see anything too far. 

Yes 20X-40X is more appropriate in daytime.

 

There really is a reason why a short refractor around 500mm focal length is ideal for daytime stuff.


Edited by luxo II, 27 November 2022 - 09:49 PM.

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