Acetal Lens Caps

[B.S.Kumar]

Like most others on the forum, I am sick of poor quality OEM lens caps. Rather than simply moan about it, I have contracted with a manufacturer to make acetal lens caps. The caps will be molded out of LG Lucel, an engineering plastic similar to Delrin. The initial samples look great. They have ribs around the circumference for better grip. The top surface is recessed so that a label can be stuck on it. The lens cap size is embossed on the surface for better readability. Finally, there are vents around the inner circumference to let air escape while attaching or removing the cap.

Sizes will range from 30mm to 105mm, in 1 mm increments. Larger sizes are possible, if there is any interest. Prices will vary according to size:
30~50mm 1,200 JPY (~12 USD / 11 Euro)
51~70mm 1,600 JPY (~16 USD / 14 Euro)
71~90mm 2,000 JPY (~20 USD / 18 Euro)
91~105mm 2,500 JPY (~25 USD / 22 Euro)
Shipping will be extra, via International ePacket service or optionally, EMS.

Since these caps will be molded, the cost of the molds means that not all sizes can be made right away. Therefore, I'd like to know from members which specific sizes would interest them most. Please choose the sizes in the poll. If you do not see a specific size please reply either on the forum, or send me an email at focusgma at gmail dot com.

Thank you.
Kumar

 

[Andre Noble]

Questions:

1) Does LG Lucel plastic outgas?

2) Are these slip-on caps that slip OVER the lens barrel/filter (similar to large format lens caps)?

3) Or are these clip-on lens caps similar to Nikon, Canon, etc caps for 35mm lenses that seat inside the lens/filter threads?

 

[B.S.Kumar]

Hi Andre,

1) No, it does not outgas. That was the main reason for choosing this material.
2) I should have clarified. These are slip-on caps, like most large format lens caps.

Kumar

 

[Andre Noble]

Hi Kumar,

You might want to include instructions on how to properly size your lens caps for any given lens filter or barrel diameter for a proper fit.

Example "If lens barrel (or filter) diameter measures 58mm, then order _______mm lens cap for proper fit. Etc."


My real life example, I recently had a lens barrel diameter of say 19mm and ordered a 19mm cap from B&H, but the cap turned out to have internal protruding ridges that allowed air flow, so with these ridges, the 19mm cap was too tight for 19mm lens diameter. In this case I should have ordered a 20mm cap or 21mm for the 19mm lens barrel diameter.

 

[B.S.Kumar]

Andre,
Thank you for your valuable suggestion.
I have given a number of unusable lenses to the manufacturer to use as masters, to ensure that the caps will fit properly. Once I have this project started, I will put up a list of lenses with the recommended lens cap sizes.

Kumar

 

[AgX]

I think snap-on caps are inprinciple the optimal ones.
(As long the lens in question got a filter thread.)

 

[Trask]

Hi Kumar,

You might want to include instructions on how to properly size your lens caps for any given lens filter or barrel diameter for a proper fit.

Example "If lens barrel (or filter) diameter measures 58mm, then order _______mm lens cap for proper fit. Etc."


My real life example, I recently had a lens barrel diameter of say 19mm and ordered a 19mm cap from B&H, but the cap turned out to have internal protruding ridges that allowed air flow, so with these ridges, the 19mm cap was too tight for 19mm lens diameter. In this case I should have ordered a 20mm cap or 21mm for the 19mm lens barrel diameter.

I second Andre's concern about nomenclature. I have a Canon RF lens that takes a 48mm cap in the threads, but I'd have to get out my calipers to determine the outside diameter of the lens -- 49mm? 50mm? I applaud your effort and would probably buy several caps, but I can see that you're going to face a real issue with how people think they should order your cap. Ideally you'd want people to measure the actual diameter of the lens the cap will slip over, regardless of the inside diameter where the threads may be, because wall thickness of the lens barrel is not uniform.

 

[B.S.Kumar]

Hi Trask,
Thank you for your support. Both you and Andre raise a very important point. Most (but not all!) lenses have a wall thickness of 1 mm at the filter threads. So if your lens has a filter thread of 48mm, the outer diameter will be at least 50mm.

The easiest and most accurate way to measure the outer diameter of a lens barrel to find the correct cap size is to place the lens face down on a piece of graph paper, aligning it to to at least two perpendicular lines. Then, using a very fine pencil, draw a circle around the barrel, and measure the diameter.

Kumar

 

[AgX]

The easiest and most accurate way would be to use a caliper, even with large diameters
(And then to thrust the diameter given by the manufacturers to be the inner diameter of the cap indeed.)

I value your effort for creating a new product, but I still not see the basic fault with existing caps.
Also I do not get the point behind your venting holes.

Likely I'm missing something.

 

[B.S.Kumar]

Yes, but not everyone has calipers, and a pencil and paper are easy to find

I keep forgetting that APUG members are not exclusively large format users. The caps that Rodenstock and Schneider supply for their large format lenses are truly pathetic. They are too thin and flexible. Many lenses have bulbous front elements, and some rear elements are almost flush with the barrel. These caps can, and do rub against the glass, damaging them permanently. Nikon and Fuji lens caps are better designed, but not all of them can be used with the German lenses. Many older lenses are odd sized, and lens caps are not easily available.

Lens caps should be just the right size. Too loose, they'll fall off. Too tight, they won't fit, or be difficult to fit or remove. If you've seen Fujinon LF lens caps, they have small ridges around the inner circumference. Those ridges ensure that there is some space between the lens barrel and the cap, and make it easy to slip the cap on and off, yet hold on to the lens. Delrin and similar plastics are more rigid than the material used in the Fujinon caps, and such ridges would not work well. Instead, there are vents cut into the inner circumference of the caps, providing the same function. Here's an image from the 3D files to better explain it.

Please let me know if you have any more questions.

Kumar

 

[AgX]

Thank you. You raised some points I did not thinbk of:

Yes, I agree with the lack of stiffness of some models.
By design even a plan push-on model could be made to accept talerances in front ring diameter.
So far flexible push-one ones are offeed off-shelf iin as great variety of diameters n 1mm increments.

I consider push-on ones good for storing a lens. For field use I so far prefer the snap-on (or rsather snap-in...) ones.
What speakes against these?

 

[David A. Goldfarb]

Very interesting initiative, particularly given the cost of, say, Schneider slip-on caps or SK Grimes caps made to order.

One thing that isn't clear from the description is that you say that they will have a recessed top surface for a label, but will leave space for bulbous front elements. Maybe you could post a photo or a drawing to show how they will work.

It might be worth researching the common sizes on existing lenses. For instance, most lenses (for a range of cameras and formats) that use a 67mm filter thread will take a 70mm slip-on cap. Of course, the ones most needed are likely to be no-longer-standard sizes that can be hard to find, as for antique large format lenses, so it would be good to compile a database of what works, once you know in practice.

 

[B.S.Kumar]

AgX, the snap-on or snap-in caps have little bits under the cap that might touch the glass. And as I discovered recently, they will not work with lenses that have slightly wider rims. Those are best suited for modern 35mm or medium format lenses.

David, I used to stick labels on my lens caps, but they would peel off, because they rubbed against other lenses in the bag. I made the recess ~1 mm so that the label would not rub against anything. Here is a very low resolution image from a 3D file. As I said, I have given the manufacturer many unusable lenses so that he can use them as masters. Once production starts with more common sizes, I will give him measurements of the older lenses I have.

Kumar

 

[David A. Goldfarb]

Looking forward to seeing how they work out!

 

[B.S.Kumar]

I've compiled a list of lens cap sizes for Fuji lenses. I'll be making similar lists for Rodenstock, Schneider and Nikkor lenses, as well as older lenses - Zeiss, Voigtlander, etc. This is certainly not complete, and I'd be glad to have more data for other lenses. Just let me know here, and I'll add them to the chart.

10 days after I posted this on various forums, the order of preference according to the polls and messages I've received is:

1. 70mm - Most Fuji lenses use that size for the front cap.
2. 80mm - Almost all of them are for Mamiya RB / RZ lenses. The general complaint is that the spring on one side breaks, rendering the cap unusable.
3. 48mm - Mainly for the older Fuji lenses
4. 67mm
5. 62mm
6. 58mm
7. 52mm

Also, I think most users seem to have asked for front caps only! LF lenses need rear caps as well, and in many cases, the rear element is relatively less well-protected. Sometimes the element is almost flush with the barrel.

The manufacturer is sending me the final samples soon, and I will share photos here. In the meanwhile, please go through the list. If there are any errors, please let me know, and I would appreciate your input on other lenses.

Thanks,
Kumar