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Swarovski SLC and Close Focus (1 Viewer)

opticoholic

opticoholic

Well-known member
Hello,
I'm curious why Swarovski limited the close focus on the 7X42 SLC's to only 13 feet. The entire SLC line has pretty poor close focus. I *know* Swarovski must have done this on purpose. Anyone care to comment?

I have read that as you improve close-focusing ability, depth of field suffers noticeably. The SLC's are indeed advertised as having very good depth of field. But I wonder what other advantages are gained by limiting the close-focus ability?

Personally, close-focus is not very high on my list of desired binocular features. Having a large sweet spot is much more important to me.

Thanks, and feel free to point me at another older thread,

--Dave
B :)
 
Hi Dave,

I suspect that the poor Close focus is due to the SLC's having been around for a long time, with the only changes being 'tinkering' with lens coatings and cosmetics. Many other manufacturers have completely revamped their models to improve the close focus. I tried a pair of 8 x30's recently, but was not happy with this problem, as I like to zoom in on Dragonflies/butterflies etc during my wandering.
Perhaps its time for Swaro to upgrade their mid-price bins properly, and move the focus wheel to the back (which also puts people off).
 
Thanks Steve,
What you say makes sense. How old IS the SLC design? 13 feet is really outside the norm these days but maybe back when the SLC was first released it was average...? I just sort of assumed they must have had their reasons for keeping the focus limit way out at 13 feet. The only advantage I've heard is that it improves depth of field. I sent an email asking Swarovski USA but who knows if I will get an answer (if I do I'll follow up here).

--DaveB :)
 
I agree with Steve, the SLC is an old design, and never allowed much additional movement of the objective for near focusing. The series started in the late 1980's, when the 8x30 Mk I was not waterproof. A flat glass was put in front of the objective, and p-coating added, to make it into the waterproof Mk II in the early 1990s. The Mk III was a redesign of the waterproofing and body shape, plus pop-up (later twist up and then removable) eyecups. The current Mk IV (i.e., SLC Neu) is the same mechanical/optical design with all its limitations. Repairs to the original Mk I and II can usually be made with parts from the Mk III and IV — resulting in a hybrid. SLC means Slim, Light, and Compact (meaning short). ;)

Incidentally, overall DOF properties don't depend on the near focus capability, which is determined by the range of movement allowed between the objective and eyepiece. The body casting constrains that. What you may be thinking of is that eye relief is inversely related to FOV. For the most part, SLCs are not really generous in eye relief, but FOV is fairly good. Overall, it's a nicely balanced set of capabilities that may not be outstanding in any one respect, but it's not seriously deficient in any way either.

Blue skies,
Ed
 
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The others have pretty much covered the subject but in short, the SLC line has remained such a success that is hasn't required or necessitated a redesign. Had the EL not been introduced they probably would have made some updates by now and that has certainly bought them another decade of mileage from the SLC. Also the field of veiw and close focusing have no bearing on one another. The field of view primarily has to do with the eyepiece in conjuction with the size of the prisms. The close focusing really just has to do with the travel limits of the mechanical focus function along with the housing dimensions.

[edit] Oops, just realized that Dave M. said DOF not FOV. Sorry I meant to say FOV also. Thanks for correcting me Henry link.
 
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I believe Dave said that he has read DOF, not FOV, is reduced by closer focus capability. That's not true. If the 7x42 SLC could focus closer than 13' that would have no effect at all on its DOF beyond 13'. The DOF would become increasing shallow at distances below 13' just like it does in any other binocular. I notice that the larger SLC's have even longer close focus: 10x50-16', 7x50, 8x50-20', 8x56-30'.
 
Thanks guys. I am by no means an expert on optical concepts. As a former teacher I know that misconceptions have a way of stubbornly surviving despite all attempts to kill them. Regarding close focus and its relation to DOF I must have read some bad information, maybe more than once. Most recently, I read this on the B&H web site, under the product description for the Bushnell 8X43 Elite:
These Elites have changed their approach, no longer having a close focusing capacity which will be the envy of the pack, but certainly not anything to slouch at with 9.0' (2.7 m). There is always a tradeoff to some degree with close focusing in a binocular; if it is too good, then you're left with too many revolutions of the focusing dial during normal use and/or a profoundly shallow depth of field.​

Anyway, thanks again very much for sharing your thoughts, and I will follow-up and tell you what SONA says, if they answer the question.

--Dave McMullen
B :)
 
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Dave,

I think the B&H writer is confused enough to be misleading. Given the same optics and focusers with the same gear ratio there will be some extra turning required with a binocular that focuses to 6' compared to 13', but all the extra turning is between 6' and 13'. Beyond 13' the turning required would be identical.

Closer focus is accomplished simply by mechanically increasing the distance between the objective and eyepiece, or in some internally focused binoculars by lengthening the backward movement of an internal focusing lens. Either way, at longer focusing distances there is no optical or mechanical difference compared to a binocular with less focuser travel. It's a bit like comparing a 2' ruler and a 3' ruler. The first 2' are identical in both.

The B&H information also seems to imply that DOF in a binocular with very close focus may be "profoundly shallow" at any distance. In fact, it will only be "profoundly shallow" at a very close distance because that's the way DOF works. In binoculars DOF is totally determined by magnification and distance. It gets shallower at shorter distance and/or with increased magnification.

Henry
 
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Hi There,

I have a pair of 10x42 SLC's and if they could focus closer than 13' I would probably lose the ability to focus at infinity when not wearing my glasses. Although I only have a -2.25 diopter correction, I have used some binoculars that will not allow me to focus completely at infinity without my glasses on. I presume that is because the manufacturers want to be able to advertize a closer focus ability and that partially is where there is a trade off.

Doug...........
 
doug el10x32 said:
Hi There,

I have a pair of 10x42 SLC's and if they could focus closer than 13' I would probably lose the ability to focus at infinity when not wearing my glasses. Although I only have a -2.25 diopter correction, I have used some binoculars that will not allow me to focus completely at infinity without my glasses on. I presume that is because the manufacturers want to be able to advertize a closer focus ability and that partially is where there is a trade off.

Doug...........
Click to expand...

oh yeah... Not being an eyeglass wearer that never ocurred to me. I forgot about people who turn the focus knob further to the right to see the same thing that I see. Hmm. I guess manufacturers really have to think about the amount of travel their optical assemblies have to allow.
 
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