Transmission % for 7x42 T*FL (1 Viewer)

7x42 FL and 8x42 HT get mentioned together, with the HT sometimes explained as an ergonomic upgrade (some don't find it an upgrade apparently) of the FL series together with Schott HT glass.

HT 95% transmission. What is the figure for 7x42 FL please?

Tom

93% according to Gijs's tests on the website of House Of Outdoor.

Allbinos transmission % for the 8x42 T*FL peaks at about 94%-95%.

The 7x42 T*FL was jury rigged from the 8x42 by giving it shorter objective tubes so we can assume its transmission % is pretty close to the 8x42. See the 8x42 transmission chart from Allbinos below.

https://www.allbinos.com/238-binoculars_review-Carl_Zeiss_Victory_8x42_T*_FL.html

Bob

Gijs has of course has published a wealth of transmission data, which can be found here: https://www.houseofoutdoor.com/verrekijkers/verrekijkers-testen-en-vergelijken/
There are lots of interesting comparisons to be made for those wanting to consider their favourite model in relation to other choices (though note the reservation below)

Specifically in relation to the OP, see ‘Testrapport Zeiss Victory HT 8×42’ from April 2013
I’ve attached 2 graphs from it showing from left to right:
- Zeiss Victory HT 8x42 vs FL 7x42, and
- Zeiss Victory HT 8x42 vs FL 8x42

A couple of observations:
- although the FL 7x42 shows generally higher transmission then the FL 8x42, there’s a strange dip at the lowest frequencies (from 450 nm), and
- the maximum difference between the 8x42 HT and FL curves is perhaps 5%, so while there's a measurable difference just how significant is it in practice?


And a more general observation, and one not intended in any way to diminish the usefulness of Gij’s work:
- objective transmission does not necessarily correspond with subjective/ perceived brightness

On one hand, for a given design (where other factors remain constant) increasing transmission will increase visible brightness
e.g. there’s lots of useful information in Gijs data about various models over time, including: Swarovski Habichts, EL SV’s and SLC HD’s and; Leica Ultravid x42’s

However, in considering perceived brightness - when comparing one brand or model to another - one also needs to take into account light/ contrast control factors such as baffling
Tobias Mennle has written extensively on this, and it's considered in most of his reviews. For a starting point see here: http://www.greatestbinoculars.com/allpages/articles/itsthebaffling.html

It’s clear from Tobias’ work - in conjunction with Gijs’ - that Leica in deciding the optical image their binoculars will have,
chooses to take a significantly different approach to that of Zeiss or especially Swarovski (for an indication, see the 3rd graph from Gijs' article showing the Leica 8x42 UV HD)

And especially when reading comparative reviews of other brands that equate subjective brightness with transmission, one needs to be mindful of the above
- there really is a lot more going on than meets the eye!


John

Here is the Russian Transmission Chart. it says the Zeiss 7x42 transmits at about 92 to 94% depending on wavelength.

https://www.birdforum.net/attachment.php?attachmentid=695397&d=1558116954

Mark, Bob, John, Dennis, thank you all.

The graphs are interesting and after looking at them and then reading John's provisos and rereading Tobias's articles it feels like I may be just starting to understand the conflicting science of brightness, contrast, and baffling. Or is it waffling?!

Tom

John A Roberts said:

although the FL 7x42 shows generally higher transmission then the FL 8x42, there’s a strange dip at the lowest frequencies (from 450 nm)

Click to expand...

John,

The dip is at the highest frequencies, i.e blue (shortest wavelengths) and the comparison is between a 7x42 FL and an 8x42 HT.
I'm not convinced that HT glass shows significant visual benefits but the measurable gains are mainly at the blue end of the spectrum and especially so if it is used in the prisms with their long glass paths.

John

Hi John,

Of course you’re right about my confusing low frequency with short wavelength (as the philosopher Simpson would say . . . D’oh!)

However, I was specifically referring to the difference in the transmission curves of the FL 7x42 and FL 8x42 - hence the second graph


John

Yes, John I see what you mean now. Perhaps the 7x42 FL with its shorter focal length objectives and steeper incident angles required a higher refractive index glass in one of the prisms than the 8x42. There is quite a difference in the transmission at the blue end of the spectrum between BK7 and BAK4.

See here: https://www.us.schott.com/d/advance...collection-datasheets-english-us-may-2019.pdf
BK7 and BK7HT are on pages 13 & 14, and BAK4 & BAK4HT are on pages 25 & 26.

It does seem though that HT glass offers small transmission benefits across most of the visible spectrum, so my assumption there was wrong.

John