[whk1992]

Is there such an adapter? I just bought myself a reverse mount for macro, which exposes the rear element of my lens. I'd like to install a filter to prevent dust from getting into the rear side or accidentally poking it when I aim at close objects. I couldn't find anything on Adorama or ebay. Perhaps I used the wrong keywords?

Thanks.

[Na Horuk]

Wait, what's the problem? Most filters allow a second filter to be screwed on, so a retroadapter should be no problem, as long as the filter threads are long enough.
I think I am misunderstanding something? Is the filter a different size than the lens threads?
Can't you try a regular step up/step down ring?

[osib]

this is what I find the best solution. Cut hole in rear cap and then put step up ring 49 to 52mm. female side goes on rear cap (it fit very tight so you don't even need to glue ring to cap) and then just screw 49mm filter.
hope this helps

[vonBaloney]

Wait, what's the problem? Most filters allow a second filter to be screwed on, so a retroadapter should be no problem, as long as the filter threads are long enough.
I think I am misunderstanding something? Is the filter a different size than the lens threads?
Can't you try a regular step up/step down ring?

They have the lens mounted in reverse so the rear element is now the front and they are looking for a way to protect it, i.e. a filter holder for the rear K-mount. I'm not aware of any such adapter, so cutting the middle out of a rear cap as suggested sounds reasonable (although I'd not sure how you'd accomplish that either on the typical hard plastic cap, sounds dangerous actually)...

[dakight]

Cutting out the cap should be easy enough with a Dremel and a burr or small sanding drum, just don't hold in in your hand while working on it. Find a way to support the inside while clamping it in a vise and wear eye protection.


Alternatively you could hold the cap against a sanding disk or grinder at an angle and rotate the cap, grinding the edge until the flat bottom separates from the ring. You could even do essentially the same thing with a sheet of course sandpaper but it would be slower.

[Not a Number]

Just buy a set of those cheap extension tubes that only has the K-mount that screw into either end of the tubes. Leave the male end off and you have a lens hood with a female K-mount.

[whk1992]

Cutting out the cap should be easy enough with a Dremel and a burr or small sanding drum, just don't hold in in your hand while working on it. Find a way to support the inside while clamping it in a vise and wear eye protection.


Alternatively you could hold the cap against a sanding disk or grinder at an angle and rotate the cap, grinding the edge until the flat bottom separates from the ring. You could even do essentially the same thing with a sheet of course sandpaper but it would be slower.

Dremel, angle grinder and pneumatic rotary cutter spin too fast and they are more likely to melt plastic than cutting through. I'll try that with a belt sander instead.

[vonBaloney]

Just buy a set of those cheap extension tubes that only has the K-mount that screw into either end of the tubes. Leave the male end off and you have a lens hood with a female K-mount.

This sounds like a better idea, although with the typical reversed lens macro setup, don't you often need to get within millimeters to focus anyway? Isn't anything at all protruding going to mess up the ability to take pictures?

[osib]

I cut my with knife that I heated, and then sanded with rasp.
it doesn't have to be a perfect circle...

[whk1992]

This sounds like a better idea, although with the typical reversed lens macro setup, don't you often need to get within millimeters to focus anyway? Isn't anything at all protruding going to mess up the ability to take pictures?

I worry about the extension tube, effectively a hood, will block ambient light and result in a very dark image.

[vonBaloney]

I worry about the extension tube, effectively a hood, will block ambient light and result in a very dark image.

It is either blocking or not blocking the lens element (i.e. causing vignetting), and if it is not than the more ambient light coming in from side angles it blocks the better (like a hood, as you say, hoods are good).

Of course it might block light on the subject itself the bigger the object you are sticking right up close to it (if not using a ring flash or something)...

[Not a Number]

It's not my idea. Credit the Extreme Macro website for this.

http://extreme-macro.co.uk/reverse-lens-hood/

You have 3 tubes so you can adjust the length. The shortest tube is usually around 5-7mm. If you look at the design of the old macro prime lenses the front element is well recessed within the barrel of the lens. On my Super-Multi-Coated Takumar Macro 50mm f/4 (screwmount) the front element is recessed around 50mm from the filter ring. I've rarely have problems with the barrel getting in the way even at 3.5x extension on my bellows. When the front standard of the bellows is reversed the lens is recessed. I have more problems with the rail getting in the way with the object than the standard of the lens. The standard has a 52mm filter thread so hoods or filters can be added.

Ambient light hitting the lens element can cause flare and reduce contrast.

From Extreme Macro:

One of the most common issues with reversed lenses is overall greyness of the final image and lack of contrast. Adding a hood is a quick fix, a cheap way to prevent excess light from straying into the image.

Extreme Macro Greyness Problems

With diffused flash macro photography, we like to have a nice large flash diffuser that covers a lot of the area from the subject's point of view. The problem is though that if light enter the lens directly from the diffuser into the lens, ie not bouncing off the subject into the lens as such, then this just registers as a uniform grey fog and gives you a low contrast photo with a bit of a washed out look. To some extent this can be corrected using levels in photoshop by adjusting the middle slider, but it can also show up as a much more difficult problem to deal with, a grey or light spot in the centre of your photo. Levels let you adjust the entire photo, but dealing with a circular highlight is a bit trickier, and the better cure is prevention.
----------------------------------

And as pointed out previously take a plastic end-cap and cut a hole it the bottom. This will protect the rear-end of the lens and also act as a lens hood.

[whk1992]

It is either blocking or not blocking the lens element (i.e. causing vignetting), and if it is not than the more ambient light coming in from side angles it blocks the better (like a hood, as you say, hoods are good).

Of course it might block light on the subject itself the bigger the object you are sticking right up close to it (if not using a ring flash or something)...

I was referring to ambient light that shine on the subject, not light that go into the lens directly.

---------- Post added 09-07-14 at 03:48 PM ----------

I cut my with knife that I heated, and then sanded with rasp.
it doesn't have to be a perfect circle...

It's not my idea. Credit the Extreme Macro website for this.

Use a hood for your reverse lens to cure greyness, low contrast and light spill

You have 3 tubes so you can adjust the length. The shortest tube is usually around 5-7mm. If you look at the design of the old macro prime lenses the front element is well recessed within the barrel of the lens. On my Super-Multi-Coated Takumar Macro 50mm f/4 (screwmount) the front element is recessed around 50mm from the filter ring. I've rarely have problems with the barrel getting in the way even at 3.5x extension on my bellows. When the front standard of the bellows is reversed the lens is recessed. I have more problems with the rail getting in the way with the object than the standard of the lens. The standard has a 52mm filter thread so hoods or filters can be added.

Ambient light hitting the lens element can cause flare and reduce contrast.

From Extreme Macro:

One of the most common issues with reversed lenses is overall greyness of the final image and lack of contrast. Adding a hood is a quick fix, a cheap way to prevent excess light from straying into the image.

Extreme Macro Greyness Problems

With diffused flash macro photography, we like to have a nice large flash diffuser that covers a lot of the area from the subject's point of view. The problem is though that if light enter the lens directly from the diffuser into the lens, ie not bouncing off the subject into the lens as such, then this just registers as a uniform grey fog and gives you a low contrast photo with a bit of a washed out look. To some extent this can be corrected using levels in photoshop by adjusting the middle slider, but it can also show up as a much more difficult problem to deal with, a grey or light spot in the centre of your photo. Levels let you adjust the entire photo, but dealing with a circular highlight is a bit trickier, and the better cure is prevention.
----------------------------------

And as pointed out previously take a plastic end-cap and cut a hole it the bottom. This will protect the rear-end of the lens and also act as a lens hood.

I have a rear lens cap that comes with my A50/1.7. Not sure if I want to destroy the original accessory, though.

[osib]

buy generic one from ebay, they are cheap...