Opticron HDF T and SDL v3 Zoom FOV (1 Viewer)

[4John]

Hi, can anyone point me to the FOV (m) for both ends of the magnfication scale for the HDF T and SDL v3 when fitted to an MM4 60. I can't seem to find the info on the Opticron website.

 

[paddyluke]

have a look at post #16 Opticron Scope and Eyepiece Focal Length Information

 

[4John]

have a look at post #16 Opticron Scope and Eyepiece Focal Length Information

paddyluke,

Thanks for the link. Unfortunately it doesn't list the SDL v3 (41270) and the AFOV for the HDF T (40862) is listed as "40~58.2" with no units, but presumably metres at 1000m, or specification of which scope it goes with i.e. 50, 60 or 77mm objective. It's odd that the information is not on the website, but perhaps it's buried somewhere and I have missed it. However, Nikon are not much better. The information for the MC II zoom I want to compare the Opticron zooms with only gives the FOV at one end of the zoom . Perhaps Pete Gamby will be along soon.

 

[Binastro]

40 to 58.2 is likely to be degrees.

40 degrees with the lowest magnification. 58.2 degrees with the highest.

It should be the same with any scope if not restricted by a field stop.

Regards,
B.

 

[4John]

40 to 58.2 is likely to be degrees.

40 degrees with the lowest magnification. 58.2 degrees with the highest.

It should be the same with any scope if not restricted by a field stop.

Regards,
B.

Binastro,

So I can calculate the FOV in metres using geometry like this ? 728m seems high. What have I missed ? Does it look like it's restricted ?


Regards

 

[BKoh]

Hi, can anyone point me to the FOV (m) for both ends of the magnfication scale for the HDF T and SDL v3 when fitted to an MM4 60. I can't seem to find the info on the Opticron website.

There is some data here about the 2 eyepieces' magnification:

41270 SDL v3 Zoom Eyepiece | Opticron

Click to view this page on www.opticron.co.uk

www.opticron.co.uk

40862 HDF T Zoom Eyepiece | Opticron

Click to view this page on www.opticron.co.uk

www.opticron.co.uk

Divide AFOV by magnification to get TFOV in degrees. Multiply TFOV (deg) by 57.3 to get TFOV in ft/1000yds, which you can divide by 3 to get m/1000m.

The HDF T is 15-45x on MM4 and 40-58°:

40° at 15x is about 2.7° or 153ft/1000yds, about 50m/1000m

58° at 45x would be 1.3°, or 74ft/1000yds, about 25m/1000m

These calculations seem to work for binos and scopes I look at, so they should be close as a first approximation.

 

[Binastro]

4 John,
The calculation would be correct at 1x magnification where TFOV is the same as apparent field of view.

BKoh,
Thanks.

There is also distortion which alters the calculation somewhat.

Regards,
B.

 

[Binastro]

The actual values need to be measured for accurate results.

The focal length of the scope will not be exactly as quoted.
The focal length of the eyepiece will not be exactly as marked.

So 15-45x maybe 16.3-46.4x.

The results may change with distance.

I use the belt stars in Orion for TFOV.
the distance from the two end stars is from memory 2.736 degrees
The distance between the middle star and one end star is from memory 1.356 degrees.
I'll look it up, but Orion is a winter constellation.

There are other star separations.

Henry gave a description for AFOV measures.

B.

 

[4John]

There is some data here about the 2 eyepieces' magnification:

41270 SDL v3 Zoom Eyepiece | Opticron

Click to view this page on www.opticron.co.uk

www.opticron.co.uk

40862 HDF T Zoom Eyepiece | Opticron

Click to view this page on www.opticron.co.uk

www.opticron.co.uk

Divide AFOV by magnification to get TFOV in degrees. Multiply TFOV (deg) by 57.3 to get TFOV in ft/1000yds, which you can divide by 3 to get m/1000m.

The HDF T is 15-45x on MM4 and 40-58°:

40° at 15x is about 2.7° or 153ft/1000yds, about 50m/1000m

58° at 45x would be 1.3°, or 74ft/1000yds, about 25m/1000m

These calculations seem to work for binos and scopes I look at, so they should be close as a first approximation.

BKoh,

Thanks. Now all I need is the AFOV for the SDL v3 so so I can compare the two. I am surprised all this is not on the Opticron website to save us all the mathematical and optical gymnastics . Perhaps the always helpful UK Opticron man Pete Gamby can oblige.

 

[4John]

Looking at another thread "Opticron e/p fov stats" it looks like my question has been asked several times before. It's unfortunate that Opticron appear to have been unwilling and/or unable to substantiate and/or quantify the words "wide" and "wider" and "widest" which appear on their site by putting the numbers on the website - unless it's buried somewhere on the site and I have missed it. This automatically leads to the suspicion they have something to hide. When I recently compared the Nikon MC 11 13-40 zoom on my ED50 side-by-side with the MM4 with HDF T and SDL v3 zooms I couldn't see any noticeable difference in the FOV, which prompted me to look at the fov on paper, which has so far confirmed what I saw - they are effectively the same.

 

[Binastro]

I don't think that Opticron are hiding anything.
Maybe they just haven't measured things.

Many binocular makers do hide things.
The Bushnell 4x21 is 3.5x21
The 5x25 is 4.4x
This is done to give the impression that they are wider field than is actually the case.

Celestron 8x30 was about 6.7x27 from memory.

The Harpia scope is sub diameter at low magnifications.

The Apo Televid 77 is about 75.5mm although the objective elements may be over 77mm out of their cell.

Astro eyepieces were often not as quoted. Maybe 10 % out even though tolerances are claimed to be less than this.

Binoculars are often vignetted or just smaller aperture than stated.
The 15x80 Steiner is about 77mm.

Some 60mm cheap binoculars are nearer 50mm.

If one is really interested the best thing is to make ones own measurements.

Or just enjoy the view and not bother to look closely at specifications.

Regards,
B.

 

[jring]

Hi,

I think we had a similar thread somewhere here when the SDLv3 came out... yes, here it is...

SDL v3 Eyepiece Now Shipping

Fair enough about the magnification on the 40809 eyepiece I just read what it said on the box regarding magnification, it didn’t refer to a Mm4 60 but a much older model scope, it was a very old NOS example I think. I tried it out as others sang its praises but it wasn’t for me and I returned it.

www.birdforum.net

Basically add small bit of fov at the high mag end and a bit more at the low mag end...

Joachim

 

[4John]

Hi,

I think we had a similar thread somewhere here when the SDLv3 came out... yes, here it is...

SDL v3 Eyepiece Now Shipping

Fair enough about the magnification on the 40809 eyepiece I just read what it said on the box regarding magnification, it didn’t refer to a Mm4 60 but a much older model scope, it was a very old NOS example I think. I tried it out as others sang its praises but it wasn’t for me and I returned it.

www.birdforum.net

Basically add small bit of fov at the high mag end and a bit more at the low mag end...

Joachim

Joachim,

Thanks for the link. Unfortunately that thread doesn't give me the numbers I am looking for.

 

[pete_gamby]

The reason that the website doesn't have field of view data is simply because of the way the databases underlying the content management system are structured.

Always happy to supply the information if requested

AFOV for the SDLv3 is 38.8~69.

Cheers, Pete

 

[4John]

The reason that the website doesn't have field of view data is simply because of the way the databases underlying the content management system are structured.

Always happy to supply the information if requested

AFOV for the SDLv3 is 38.8~69.

Cheers, Pete

Pete,

Thanks. Is that degrees or m/1000m ? Can you give me the same information for the HDF T as well please ?

Is the AFOV in m/1000m the same for your 50, 60 and 77mm scopes ?

Several others have asked for this sort of information on previous threads, so it might be more efficient in the long term to link the FOV data to the website instead of dealing with requests piecemeal via this forum. Perhaps it's one for the suggestion box when time and budget permit.

Regards

 

[Binastro]

It will be degrees.

The AFOV applies to the eyepiece and should be the same in any telescope unless something restricts the view.

Regards,
B.

 

[jring]

Joachim,

Thanks for the link. Unfortunately that thread doesn't give me the numbers I am looking for.

Hi,

as copied from the document in the post I linked above:

	mag	true fov	apparent fov
			manu specs	measured
Opticron SDL2	18​	1.8​		35​
	25​			47​
	36​			58​
	54​	1.2​		68​
Opticron SDL3	18​	2​		41​
	25​			55​
	36​			61​
	54​	1.3​		72​

Please note that these will be slightly different from what Pete has stated as these were measured by a forum member before specs were available.

And as has been noted, apparent field of view or afov is always given in degrees, true field of view (roughly afov/mag) can be given in deg too. Or convert to whatever units you prefer - multiply by 17.5 for m/1000m or by 52.5 for ft/1000yd.

Cheers,

Joachim

 

[GrampaTom]

Shopping for scope recently and putting together my own spreadsheet of specs, I noticed Opticron FOV was no where to be found. I emailed them and Pete kindly and rapidly responded. Thanks again Pete. Heres what he sent:

MM4 77 w SDLv3 18-54, FOV 105-69
MM4 77 w HDF T 18-54, FOV 93-48
MM4 60 w SDLv3 15-45, FOV 141-93
MM4 60 w HDF T 15-45, FOV 138-62

Adjusting for magnification differences, these are pretty close, seems.