scopes-does size matter? (1 Viewer)

paddy7 · May 23, 2017

Several points occurred to me all at once just now: the memory of someone years ago saying 'get good bins, but an excellent scope'; the danger of trying to fulfill all your needs at once (e.g. a 50mm and a 95mm); the danger of spreading the available funds across two 'reasonable' devices rather than getting one good one, and the old expression 'second best leads to second thoughts.'
The requirement you have for scopes is an evolution; as mentioned above, a very good 65mm may serve you for years before you find a need for something bigger.

Andy Adcock · May 23, 2017

jring said:
Thank you!

Joachim

I don't get the point, if you are zoomed in at x35, the FOV will be narrower than if you had the ability to zoom out to say x20 hence the ability to do so is advantageous?

Physics never was my strong suite, surely any zoomed image has a narrower view than non zoomed, the only variable being the width of the objective lens on any given scope, in my case 78mm?

A

Andy Adcock · May 23, 2017

Alexis Powell said:
Only if your zoom gives a wider true FOV than your fixed, which is often not the case. Did you read jring's post (i.e. see the numbers there)?

--AP

I have no idea what those numbers represent, I'm a birder not an optician.

Go to a Birdfair and do some field tests i.e try finding a small bird that's 25m away in a hedge or woodland with few, obvious points of reference, lower mag is always easier simply to locate the bird, I don't see how anyone with any field experience could argue that?

A

Binastro · May 23, 2017

Zoom eyepieces have narrower AFOVs at lower magnification than at higher magnifications.

This is because lower magnification means longer focal length eyepiece.
The field is determined by the front field lens, actually the field stop.

In spotting scopes the eyepiece ends are narrow, although astro refractors have 2 inch barrels, and my 123mm objective f/5 has a 3 inch barrel.

When designing a large FOV fixed focal length eyepiece one makes full use of the eyepiece barrel diameter.

jring · May 23, 2017

andyadcock said:
I have no idea what those numbers represent, I'm a birder not an optician.

Go to a Birdfair and do some field tests i.e try finding a small bird that's 25m away in a hedge or woodland with few, obvious points of reference, lower mag is always easier simply to locate the bird, I don't see how anyone with any field experience could argue that?

A

Hi,

that's why I didn't use optics talk like angular tfov or even afov but the linear field of view as given for binoculars in m at 1000m.
Just imagine you are looking at a fence with distance marks from a distance at 1000m.

For the small body Kowas, the normal zoom at the highest mag of 60x will show you 18m of the fence. If you zoom out to 20x, the field of view will be wider and you will see 33m of the fence.

Had you used the 30x wide EP instead, it would have shown you 42m oft the fence. Of course you can't change magnification here, but for hedge and woodland 30x should be plenty.

As for the reasons why zooms are usually quite narrow at the low mag end, see Binastros post.

Joachim

Alexis Powell · May 23, 2017

andyadcock said:
...surely any zoomed image has a narrower view than non zoomed...

I have read all your posts, but I assure you with the greatest respect that you do not understand something important. Field of view (FOV) generally decreases as magnification increases, but the two are independent of each other to a fair amount. You are right that when you compare the view through any particular zoom eyepiece that it will have a wider true FOV at low power (making it easier to find things) than at high power. What you don't seem to understand is that a fixed wide-angle eyepiece can have a much wider FOV at a given magnification than a zoom would at that same magnification, or even when the zoom is set at a lower magnification. I use a fixed 30x wide field eyepiece with my Nikon scope. It provides a substantially wider view at 30x (the view is a circular area 126 ft across at 1000 yards) than does the available zoom at its lowest power of 25x (the view is a circular area 84 ft across at 1000 yards), so it is much easier to find birds with the 30x than with the zoom set to 25x. The numbers differ a bit from brand to brand, but this comparison is typical of many scope systems. Some of the new top-end zoom eyepieces are designed to have a fairly competitive FOV at each magnification compared to fixed power eyepieces, but most on the market do not. It is also the case that not all fixed power eyepieces are wide angle designs. A modern wide-angle zoom can do better than a non-wide fixed, but that is a comparison of rare occurrence.

--AP

Andy Adcock · May 23, 2017

Practice beats numbers every time, I'm speaking with 30 years field experience of using scopes and I can tell you that any object is more easily found at lower magnification.

It's fine in a big open space with a few points of reference to work with but try it in a dark forest.

Most birders will reduce the zoom to minimum for locating the object and zoom in once found, this is why I consider that personally, buying a fixed x35 was a mistake, especially given that my scope has an eye piece that is offset from centre, it's the worst scope I've ever had for findin stuff, Kowa TSN-823

A

Binastro · May 23, 2017

The reason why a low power finds things is that the exit pupil is bigger and the image brighter.
In a dark location this will be important.

As to offset eyepieces or for that matter monoculars, which look like half Porro prism binoculars, they are indeed difficult to find things.

Alexis Powell · May 23, 2017

andyadcock said:
Practice beats numbers every time, I'm speaking with 30 years field experience...

Ha! Now this is getting ridiculous. Of what use is experience if you are unable to assimilate new information (i.e. learn)?

Since it seems to matter to you, I can assure you that many members on BirdForum have at least 30 years experience, if not far more, with scopes (of many models/brands) in the field.

Tell me how using my zoom at low power (25x) would be superior to my fixed 30x for finding birds when the field of view of the 30x is more than twice the area (225% larger, to be precise) of the zoom at 25x.

Previously, you said you had a 78mm scope, with a 35x eyepiece. The Kowa TSN-823 is an 82 mm scope, and I didn't know that a 35x was ever made for it (at least by Kowa). A 20-60 zoom eyepiece is available for that scope, but I would suggest the 32x wide angle for everyday use. It's a really nice scope. If you are having trouble leaning to point it, I suggest you learn how to make a cable tie (or as we call them here, zip tie) sight. Read these threads:

http://www.birdforum.net/showthread.php?t=99084
http://www.birdforum.net/showthread.php?t=166747

What is clear to me is that you may have logged 30 years experience using scopes (or rather, a scope or two?), but you have not gained much practical or theoretical understanding in that time. Either that, or you are an internet troll. Best of luck to you, and to anyone who takes your misguided advice to heart. I hope some of what has been discussed above is of use to other readers.

--AP

jring · May 23, 2017

andyadcock said:
Practice beats numbers every time, I'm speaking with 30 years field experience of using scopes and I can tell you that any object is more easily found at lower magnification.

It's fine in a big open space with a few points of reference to work with but try it in a dark forest.

Most birders will reduce the zoom to minimum for locating the object and zoom in once found, this is why I consider that personally, buying a fixed x35 was a mistake, especially given that my scope has an eye piece that is offset from centre, it's the worst scope I've ever had for findin stuff, Kowa TSN-823

Hi,

a few things to try for better sighting:

- try Kimmo's brilliant cable tie sighting device - when I know where the bird is it takes a second or two to peep over EP eyecup and the cable tie and I'm on target even at max magnification:

http://www.birdforum.net/showthread.php?t=99084

- if you really want a zoom for the 823, the fitting 20-60 was called TSE-Z7B and offers a field of 35m/1000m at 20x and 17.5m/1000m at 60x. Your 32x EP (called TSE-14WB) shows 38.4m/1000m for comparison. Locating a used one might be difficult and they're unavailable new. Isn't the wayback machine a great thing - facts from 13 years ago at your fingertips!

- Kowa still offers an adapter called TSN-EC1A which lets you adapt the EPs for the current Kowa small body scopes to the Kowa 823. Due to the slightly longer focal length of 450mm for the 823 as compared to the 420mm of the small body scopes, this would result into 21.5-64x magnification and a field of 31-16m/1000m - for comparison - your current 32x wide has 38.4m/1000m. The catch is that the adapter is 89€ plus 300€ or so for the current zoom TSE-Z9B.

Cheers,

Joachim

paddy7 · May 24, 2017

Interesting points, and something that tbh i hadn't considered before. However, on a recent field trip, i looked through a friend's older Swaro ATS 65 with a fixed 30x eyepiece, then through my own, with the 25-50X WA zoom (with it set at around 30x) and the FOV through his was noticeably wider.
I believe this is the point being made here - that a zoom eyepiece will not be as wide a FOV as a fixed, at the same magnification. I'd still rather have the zoom though!

dalat · May 24, 2017

andyadcock said:
Practice beats numbers every time, I'm speaking with 30 years field experience of using scopes and I can tell you that any object is more easily found at lower magnification.(...)

buying a fixed x35 was a mistake, especially given that my scope has an eye piece that is offset from centre, it's the worst scope I've ever had for findin stuff, Kowa TSN-823

Haha, Andy, you're giving people here a hard time.

I think nobody tries to tell you that what you see with your zoom and fixed eyepieces is wrong. It's correct. But you can't make a general rule out of your 30 years of experience with these two eypieces, because there are other eypieces out there that behave diffently. If you want to compare FOV of different eyepieces, just look at the numbers (how many meters of FOV 1000 m away) given by the manufacturers, and all is clear.

As for your aiming troubles (we discussed that in another thread already), looking at photos of your scope, isn't there an aiming aid next to the eyepiece (this little tube). That does not help?

Andy Adcock · May 24, 2017

dalat said:
Haha, Andy, you're giving people here a hard time. I think nobody tries to tell you that what you see with your zoom and fixed eyepieces is wrong. It's correct. But you can't make a general rule out of your 30 years of experience with these two eypieces, because there are other eypieces out there that behave diffently. If you want to compare FOV of different eyepieces, just look at the numbers (how many meters of FOV 1000 m away) given by the manufacturers, and all is clear.

As for your aiming troubles (we discussed that in another thread already), looking at photos of your scope, isn't there an aiming aid next to the eyepiece (this little tube). That does not help?

I'm on the point of changing it Florien,
that's why I'm asking about the modern counterpart.

The paint has all gone tacky and there's something floating around inside which is probably going to do damage to the optics.

Kowa no longer have a service centre in the UK, that would make repair a lengthy and expensive process?

A

paddy7 · May 24, 2017

Can't comment on expense, but i sent an eyepiece back to Kowa via CleySpy earlier this year (the dreaded paint flecks), expecting a 6-8 week turnaround and it was back in 3. Went to Germany (under guarantee though).

Andy Adcock · May 24, 2017

paddy7 said:
Can't comment on expense, but i sent an eyepiece back to Kowa via CleySpy earlier this year (the dreaded paint flecks), expecting a 6-8 week turnaround and it was back in 3. Went to Germany (under guarantee though).

Mine is 10 years old so I guess the warranty is up, can't even remember where I bought it from.

Really want to change it for an inline eye piece though and that's another pain in the arse, it seems that none of the older eye pieces fit the new scopes, more expense!

A

paddy7 · May 25, 2017

Maybe - and trying to draw the aspects of this thread together - it may be worth thinking about the Swaro ATX 65 as a starting point? It's heavier than the old ATS65 and definitely more expensive, but gives you the option of going bigger later by getting one of the bigger objective modules? If you're looking at expense either way, it's an option......

Andy Adcock · May 25, 2017

paddy7 said:
Maybe - and trying to draw the aspects of this thread together - it may be worth thinking about the Swaro ATX 65 as a starting point? It's heavier than the old ATS65 and definitely more expensive, but gives you the option of going bigger later by getting one of the bigger objective modules? If you're looking at expense either way, it's an option......

Currently considering the TSN-883, it's a long term investment so I see no point in compromising on quality and spec?

A

edwincjones · May 25, 2017

I want to thank everyone who has responded --this has been very informative and useful

edj

CSG · May 26, 2017

I almost bought a Swaro ATS65 but for very little more was able to acquire the Kowa TSN-883 and find that for my needs, it's more than portable enough. While I mostly use a Televue TV-85 for astronomy, the Kowa is more than satisfying where I don't thing the Swaro would have been. Compared to the weight of the TV, the Kowa is a featherweight. Using a CF tripod helps as well.

Bottom line, unless you're humping a scope for a long ways, bigger is better.

paddy7 · May 26, 2017

CSG said:
I almost bought a Swaro ATS65 but for very little more was able to acquire the Kowa TSN-883 and find that for my needs, it's more than portable enough. While I mostly use a Televue TV-85 for astronomy, the Kowa is more than satisfying where I don't thing the Swaro would have been. Compared to the weight of the TV, the Kowa is a featherweight. Using a CF tripod helps as well.

Bottom line, unless you're humping a scope for a long ways, bigger is better.

Certainly true - the Kowa is only about 1lb imperial more than the ATS. I prefer the ATS 65 for travel though, as it's a more robust instrument. I've known three Kowas to crack at the 'shoulder' on the angled version, particularly if toppling backwards. I've forgotten how many times the Swaro has been over, with no trouble. Fits in cabin luggage easier too.

scopes-does size matter? (1 Viewer)

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