Join for FREE
It only takes a minute!
Zeiss - Always on the lookout for something special – Shop now

Welcome to BirdForum.
BirdForum is the net's largest birding community, dedicated to wild birds and birding, and is absolutely FREE! You are most welcome to register for an account, which allows you to take part in lively discussions in the forum, post your pictures in the gallery and more.

Showing results 1 to 25 of 967
Search took 0.06 seconds.
Search: Posts Made By: John Russell
Forum: Binoculars Friday 20th June 2014, 17:00
Replies: 26
Views: 4,099
Posted By John Russell
No, Brock, I just used the edge condition as a...

No, Brock, I just used the edge condition as a basis for the "explanation" but pointed out in post #8 that astigmatism gets progressively worse towards the edges because the tangential and sagittal...
Forum: Binoculars Thursday 19th June 2014, 13:02
Replies: 26
Views: 4,099
Posted By John Russell
Brock, I think "bad" is a little strong,...

Brock,

I think "bad" is a little strong, undesirable would be better.
All bins probably have some astigmatism to a greater or lesser extent, though I can't see any in my 10x42 SV, and that's good...
Forum: Binoculars Wednesday 18th June 2014, 14:26
Replies: 26
Views: 4,099
Posted By John Russell
No idea what that's got to do with optics....

No idea what that's got to do with optics. Perhaps the author was the sole occupant of my ignore list ;).

John
Forum: Zeiss Wednesday 18th June 2014, 10:45
Replies: 77
Views: 18,173
Posted By John Russell
Henry, What a typically clear and simple...

Henry,

What a typically clear and simple demonstration!
Perhaps you got the World Cup special edition for Italian fans. It does look like their flag out at the edges.

John
Forum: Binoculars Tuesday 17th June 2014, 22:40
Replies: 26
Views: 4,099
Posted By John Russell
Along with field curvature (not to be confused...

Along with field curvature (not to be confused with distortion) it's the cause of a progressive sharpness loss towards the field edge. Unlike field curvature it cannot be corrected by...
Forum: Binoculars Saturday 14th June 2014, 17:27
Replies: 26
Views: 4,099
Posted By John Russell
Astigmatism as an Aberration in Optics

There is often confusion between astigmatism of the eye and astigmatism as an aberration in an optical instrument, so I thought I would attempt an explanation. It has even been suggested that one...
Forum: Tripod and Heads Saturday 14th June 2014, 14:14
Replies: 38
Views: 18,932
Posted By John Russell
Kimmo, I was unaware of the introduction of the...

Kimmo,

I was unaware of the introduction of the Sirui VH-10 and VH-15 heads, which would appear to be another couple of nails in the coffins of the established manufacturers.

I have a Sirui L-10...
Forum: Binoculars Saturday 14th June 2014, 12:14
Replies: 82
Views: 9,585
Posted By John Russell
I took this step months ago and would encourage...

I took this step months ago and would encourage anyone interested in furthering their knowledge on Birdforum to do likewise.

I wish he'd go away and start an American branch of...
Forum: Swarovski Saturday 14th June 2014, 11:33
Replies: 15
Views: 4,577
Posted By John Russell
Brock, That's conceivable but, in view of...

Brock,

That's conceivable but, in view of Swarovski's service reputation, I think unlikely.

John
Forum: Tripod and Heads Saturday 14th June 2014, 10:55
Replies: 38
Views: 18,932
Posted By John Russell
Probably not, but AFAIK that was not the OP's...

Probably not, but AFAIK that was not the OP's requirement.

John
Forum: Swarovski Friday 13th June 2014, 23:13
Replies: 15
Views: 4,577
Posted By John Russell
Well, you could try Orniwelt. Their German prices...

Well, you could try Orniwelt.
Their German prices would correspond to 1634 and 1679 for 8x56 and 10x56 respectively without sales tax.
You would of course have to pay shipping and your own import...
Forum: Tripod and Heads Friday 13th June 2014, 22:45
Replies: 38
Views: 18,932
Posted By John Russell
See post #4. The Berlebach 510 weighs 700 g, not...

See post #4. The Berlebach 510 weighs 700 g, not much heavier than a Manfrotto 700 RC2, and better in every way.
There would be no point in stacking an Arca-swiss adapter on top of another QR system...
Forum: Tripod and Heads Thursday 12th June 2014, 21:01
Replies: 38
Views: 18,932
Posted By John Russell
For the past two or three years I have used a...

For the past two or three years I have used a Berlebach 552, which uses Arca-Swiss plates.

It is stable, lightweight (820 g) and very well made (all CNC) and is rated up to 6 kg. There is adjustable...
Forum: Zeiss Wednesday 4th June 2014, 14:46
Replies: 43
Views: 16,656
Posted By John Russell
Lee, Many thanks for the excellent review. It's...

Lee,

Many thanks for the excellent review. It's often suggested that the 15x56 format is a very specialised market but the interest this thread (and a review of the 15x56 SLC on Cloudy Nights) has...
Forum: Binoculars Saturday 31st May 2014, 20:40
Replies: 7
Views: 1,909
Posted By John Russell
I would say that the eye relief of the 10x42...

I would say that the eye relief of the 10x42 Meostar will almost certainly be inadequate for glasses wearers.
The size of the eye lens is a fairly good indication of eye relief; see this thread:...
Forum: Kowa Friday 30th May 2014, 15:24
Replies: 33
Views: 20,649
Posted By John Russell
Malcolm, I have used three different astro...

Malcolm,

I have used three different astro adapters on Zeiss Diascope and a Swarovski ATM scopes, so I think you have some options, even if you are going to have to get something made.

A Kowa...
Forum: Binoculars Thursday 29th May 2014, 16:08
Replies: 6
Views: 1,553
Posted By John Russell
Zeiss Lens Wipes

These will be familiar to many but as questions about lens cleaning crop up frequently, I thought it worth a mention.
I came across them at my local drug store and they were no more expensive than...
Forum: Kowa Thursday 29th May 2014, 11:02
Replies: 33
Views: 20,649
Posted By John Russell
Malcolm, You should estimate the diameter of the...

Malcolm,

You should estimate the diameter of the "window" in the scope body under the eyepiece.
There would be no point in using eyepieces with a larger field stop than this as they would...
Forum: Kowa Thursday 29th May 2014, 10:44
Replies: 2
Views: 2,704
Posted By John Russell
Thanks for those insights, Henry. In view of the...

Thanks for those insights, Henry.

In view of the price differences and the marginal optical advantages (and some physical disadvantages) of CaF2 over FPL-53 and similar fluorite crown glasses from...
Forum: Kowa Wednesday 28th May 2014, 17:45
Replies: 2
Views: 2,704
Posted By John Russell
The Price of Fluorite (Calcium fluoride)

I recently received a catalogue from Edmund Optics in which they are offering plano-convex fluorite lenses (uncoated) in diameters ranging from 12,5 mm to 50 mm for scientific applications. They have...
Forum: Zeiss Monday 26th May 2014, 17:53
Replies: 156
Views: 30,537
Posted By John Russell
Well, Lee I know it doesn't offer any significant...

Well, Lee I know it doesn't offer any significant advantages, but there is a BaK4HT and also a SK2HT, which could conceivably be used in SP prisms.

HT now seems to be chasing ED, SD etc. as a...
Forum: Zeiss Sunday 25th May 2014, 23:45
Replies: 156
Views: 30,537
Posted By John Russell
The dealer, Orniwelt has often jumped the gun in...

The dealer, Orniwelt has often jumped the gun in the past.
They're not showing anything new but they're showing the FLs as discontinued, so it looks like it's going to be 32 mm HTs.

John
Forum: Spotting Scopes & tripod/heads Wednesday 14th May 2014, 23:45
Replies: 12
Views: 3,022
Posted By John Russell
Lars, I believe the Celestron scope takes 1,25"...

Lars,

I believe the Celestron scope takes 1,25" astronomical eyepieces, which allow a maximum field stop of 27 mm.
If the focal length is 540 mm the maximum achievable FoV would be around 2,9,...
Forum: Leica Sunday 2nd March 2014, 22:34
Replies: 7
Views: 6,277
Posted By John Russell
Hi Frederico, I have just checked a Leica...

Hi Frederico,

I have just checked a Leica catalogue, which specifies E67.
I think this must be M67 x 0,75 as there don't seem to be any other pitch sizes in that filter thread diameter.

John
Forum: Leica Friday 14th February 2014, 14:07
Replies: 17
Views: 6,290
Posted By John Russell
I'm relieved to see that Brock survived that...

I'm relieved to see that Brock survived that video.
I would have thought the rolling ball in those panoramic sweeps of the interior would have given him palpitations!

John
Showing results 1 to 25 of 967
 


Fatbirder's Top 1000 Birding Websites

Help support BirdForum

Page generated in 0.23002410 seconds with 10 queries
All times are GMT. The time now is 08:40.