80mm vs. 100mm (1 Viewer)

[Pepitogrillo]

Hello,
I seek advice.
It turns out that most of the observations I make are made in a static position, lagoons, ponds, lakes, fixed places... rather than moving from here to there...
Sometimes I notice that with an 80mm I lack some light,
My question is, if it would be worth going to a 100mm..
I also do some casual astronomical observations.
Nice to hear your opinions.
Best regards
Tico.

 

[Binastro]

Hi Tico,

If you travel by car and don't have to carry things, I would go with 120mm or maybe 100mm.

My standard terrestrial scope was a 150mm Maksutov Cassegrain with oversize primary.

But a modern ED 120mm would do well, maybe with a Baader fringe killer or semi apo filter for astro and maybe terrestrial.

If you have to carry things a long way, it depends how strong you are.

Regards,
B.

 

[Tringa45]

Hi Tico,

I think it will be difficult to achieve a significant improvement over a good 80 mm birding scope. The present state of the art are probably the Kowa 883/884 or Swarovski ATS/STS 85 or 95. There has been some disillusionment here on the forum with the Swarovski 115 mm module and also Kowa TSN-99, both of which failed to meet expectations.
The only other 100 mm scopes worthy of mention are the Optolyth (if available) and the Pentax. At its lower magnifications the Zeiss Harpia does not provide the exit pupil size one would expect from its objective diameter.
The maximum resolution of the human eye is at around 2 mm pupil size, so there is a loss of brightness and diminishing returns for terrestrial magnifications where exit pupil size is smaller than that. Atmospheric conditions will also place a limit on magnification unless you have an elevated position or are close to the water's edge.
Of course, big astro refractors could provide a theoretical advantage in brightness and resolution, but they are heavy, not waterproof and have a reversed left to right image with an erecting mirror or prism, which would make them unsuitable for birding. To my knowledge there are no good 45° Amici prisms which would work well at high magnifications.

John

 

[wllmspd]

I’m perfectly happy using a William optics prism on an 80mm APO, at very high power on plenty there is a lovely diffraction spike from the prism edge, but otherwise the views are just fine. Big Astro refractors also are rather long and so less easy to pop in a backpack.

Peter

 

[KevinL]

Generally speaking, more aperture gives better brightness and resolution if all other things are equal. For example a Celestron Regal m2 100mm should be brighter and have slightly better resolution than the 80 mm model. They are also heavier though which means less portability and may mean a sturdier tripod. So if your priority is a brighter image and a bit more resolution and youre ok with the added weight then go with a larger aperature scope. That said, you should not expect a lower quality scope with a wider aperature to out perform a higher quality scope with smaller aperature. I have a couple scopes that I have bought over time that gives me flexibility. I have a light weight 60mm alpen scope for packing and trail use, I have an 85 mm vortex razor scope for longer range work and a 127 mm Celestron C5 asto scope for the longest range views or the most magnification from the vehicle.

 

[jcwu88]

Hi, Tico,
My suggestion is to try 100mm or purchase one with good return policy with side by side comparing with your current scopes.
I used to have Nikon Fieldscope ED82 and upgraded to Kowa 99A. Side by side comparison would show the difference. Then it’s up to you whether the upgrade is worthy.
There is definitely sample variations in these scopes even alpha brands. I am lucky to have a nice 99a sample so I decided to upgrade from 80ish to 100ish.
About sample variation, you can find a lot of tests and information in these forum.

Good luck on your scope searching,

Jay

 

[KevinL]

Another alternative is to step up in quality. What are you currently using? Could you move to the next tier up? Going up a level or two usually gives you higher light transmission numbers for a brighter image. Oh and another thought, most sporting spotters, even high end ones are rather poor performers at night, so if you are serious about use for astronomy, it might do you well to get a smaller astronomy scope and use it in day time. My C5 is a slightly better terrestrial and much better astro scope than my Vortex Razor 85mm hd scope. Probably due to the larger aperature.

 

[Pepitogrillo]

Thanks, but the C5 is not water proof?

 

[Hermann]

Thanks, but the C5 is not water proof?

No, it isn't. Not at all.

Hermann

 

[Pepitogrillo]

But during the day, the advantage of the 100mm over the 80mm is very noticeable?

 

[DRodrigues]

But during the day, the advantage of the 100mm over the 80mm is very noticeable?

If you want to use >60x and don't have heat-waves problems, probably yes. See CR-telescopes and specially 100mm spotting scopes and Preferred CR-telescopes - still didn't updated the page with the X115 that I'm using recently...

 

[KevinL]

Thanks, but the C5 is not water proof?

That is one of the disadvantages of the C5. It is not water proof. You have to assemble it before use. It weighs 6 lbs so it needs a strong tripod It is more delicate than a sporting scope also. So yes it has its tradeoffs. It is also not as easy to point onto target because it requires a finder scope. Mine still has the original finder which was poor quality but it's functional. It originally came with a 25 mm eyepiece which gives 50x. Thereafter I bought a Baader hyperion zoom eyepiece which gives 52x -124x. The zoom is usable all the way to 124x if seeing conditions are good. But the image quality does get a little soft beyond 12mm which is roughly 104x or so. With the C5 side by side with the vortex razor at 50x, the C5 is noticably brighter, and the resolution is close but the C5 wins. The image contrast and color is just a touch better in the razor. The razor tops out at 60x and I feel like for me it is usable up to 60x. The C5 starts at 50x and has magnification up to 124x so for me it picks up where the razor leaves off. The Razor of course can zoom back to 20x but the C5 can only go down to 50, and perhaps a little lower if I had a different eyepiece. I picked up my C5 used for $250 which is a lot of performance for the price. The Baader zoom was $300 used also. So for $550 total I got optical performance that rivals or bests the best sporting spotters. The Vortex Razor in contrast typically runs $1200-$1400 new and can be had for $700-$800 used. So there are advantages and tradeoffs with the C5 vs sporting scopes. I find use for both in different situations.

 

[sillyak]

That is one of the disadvantages of the C5. It is not water proof. You have to assemble it before use. It weighs 6 lbs so it needs a strong tripod It is more delicate than a sporting scope also. So yes it has its tradeoffs. It is also not as easy to point onto target because it requires a finder scope. Mine still has the original finder which was poor quality but it's functional. It originally came with a 25 mm eyepiece which gives 50x. Thereafter I bought a Baader hyperion zoom eyepiece which gives 52x -124x. The zoom is usable all the way to 124x if seeing conditions are good. But the image quality does get a little soft beyond 12mm which is roughly 104x or so. With the C5 side by side with the vortex razor at 50x, the C5 is noticably brighter, and the resolution is close but the C5 wins. The image contrast and color is just a touch better in the razor. The razor tops out at 60x and I feel like for me it is usable up to 60x. The C5 starts at 50x and has magnification up to 124x so for me it picks up where the razor leaves off. The Razor of course can zoom back to 20x but the C5 can only go down to 50, and perhaps a little lower if I had a different eyepiece. I picked up my C5 used for $250 which is a lot of performance for the price. The Baader zoom was $300 used also. So for $550 total I got optical performance that rivals or bests the best sporting spotters. The Vortex Razor in contrast typically runs $1200-$1400 new and can be had for $700-$800 used. So there are advantages and tradeoffs with the C5 vs sporting scopes. I find use for both in different situations.

The advantages you list for the C5 apply to most telescopes in general vs. Spotting scopes.

For example a cheap 80mm Chinese FPL-53 refractor, with a decent quality mirror diagonal and a good telescope eyepiece will equal or beat any alpha spotting scope of the same size. However it is heavy, has a reversed image, not weather proof, clunky and slow to put together etc. However optical quality for dollar spent is very good.

 

[jcwu88]

The advantages you list for the C5 apply to most telescopes in general vs. Spotting scopes.

For example a cheap 80mm Chinese FPL-53 refractor, with a decent quality mirror diagonal and a good telescope eyepiece will equal or beat any alpha spotting scope of the same size. However it is heavy, has a reversed image, not weather proof, clunky and slow to put together etc. However optical quality for dollar spent is very good.

Agree. Astro scopes and spotting scopes are two different type of instruments.

Spotting scopes require lightweight, compact, and waterproof. Manufacturers squeezed objective, focusing lens, image erecting prisms, and sometimes focal extender in a closed weatherproof body. The system is way more complicated than astro refractors. Light passes through many lens and multiple reflections in the prism.

Astro refractors, on the other hand, are much less complicated. Focusing is by moving eyepieces to focal plane; 90 degree mirror/prism star diagonals usually have only one total-reflection surface. Light passes less lens and reflection surfaces than spotting scopes.

Given same quality of coatings, astro refractors easily outperform the spotting scopes due to the different complexity of optical components.

I found the astro scope Skywatchers ED 80 with good astro eyepieces is optically on par with Kowa 99A. But I will choose 99A without hesitation when I need to carry scopes and tripods in the muddy field. Spotting scopes are designed for this purpose.

 

[KevinL]

Right, so while my C5 can hang with and even best the top spotters, I would readily trade it for a Swarovski or Zeiss spotter.