[jawats]

All,

I have the Tamron A001, which is a very decent lens, all around. Recently, in doing astro images, the group (and I) noted that there was serious vignetting going on in the images. I do not notice it in single shots, but in multiple / stacking, it definitely becomes a thing.

Now, I notice that there is a baffle at the end of the lens. I was going to post some photos, but realized that the old sale ad here has some excellent examples of the baffle.

I was wondering if performing an operation similar to this: Modifying the DA* 60-250mm F4 for Full Frame - Introduction - In-Depth Articles might result in better images?

The Canon, Nikon, and Sony mount versions of this lens do not have the baffle in place. Pentax versions on eBay and here show the baffle. I have attached a sample showing the vignetting - it happens with and without the 1.4x TC.



Thoughts?

--Jonathan

[ProfessorBuzz]

Consider Flat Field corrections. Not much you cna do about hhe assembly of the lens. Keep in mind the flange focal distance is different between cameras, and the entry path behind the mounting ring on the body is smaller on Pentax, so they had to accomodate that. This is why you'll see plenty of astrophotography M48x0.75 T-rings for Canon and others, and most T-rings for Pentax are M42x0.75 - there just isnt room.

[UncleVanya]

That’s extreme vignetting indeed… I’d say you have little to lose in trying to modify the baffle or replace it.

[BigMackCam]

I'm not entirely sure this is vignetting... It could be, but I'm just not 100% convinced. Why? Firstly, the vignetting looks too hard - i.e. the transition isn't gradual. Secondly, it looks more like the contrast in that central area is lower than the supposedly-vignetted part of the frame. Is it possible there was moisture - condensation, for instance - in the lens? I vaguely recall something like this happening to me in the past, where condensation collected in the centre of the front or rear lens element, causing a circular area to look "misty"...

One question - did you have any filter fitted to the lens?

---

Last edited by BigMackCam; 11-07-2021 at 07:40 AM.

[jawats]

I'm not entirely sure this is vignetting... It could be, but I'm just not 100% convinced. Why? Firstly, the vignetting looks too hard - i.e. the transition isn't gradual. Secondly, it looks more like the contrast in that central area is lower than the supposedly-vignetted part of the frame. Is it possible there was moisture - condensation, for instance - in the lens? I vaguely recall something like this happening to me in the past, where condensation collected in the centre of the front lens element, causing a circular area to look "misty"...

One question - did you have any filter fitted to the lens?

BMC,

I did not have any filter on the lens.

Would letting the lens sit out in the cooler (now) air to adjust help? Or would I consider something like a dew heater on the lens? I do not recall seeing anything inside the lens (though I did not look carefully).

[Bob 256]

Condensation is caused by a cold lens and moisture condensing on it. Setting the lens in a cooler wouldn't help - might make it even worse if the cooler has a high relative humidity. Best thing is a dew heater if this is the issue. If the moisture is internal, a dew heater will help but the problem might persist. Store your lens in a poly bag with a bag of desiccant, and over time, it should draw out any internal moisture, though it might take a while. In any case, a dew heater is worth a try.

Moisture in the lens is caused by bringing a cold lens into a heated environment without bagging. Moisture in that environment will condense on the cold surfaces and any air drawn into the lens will bring moisture with it. It's good practice to bag a lens with desiccant which will prevent moisture from accumulating in your lens.

[jawats]

Condensation is caused by a cold lens and moisture condensing on it. Setting the lens in a cooler wouldn't help - might make it even worse if the cooler has a high relative humidity. Best thing is a dew heater if this is the issue. If the moisture is internal, a dew heater will help but the problem might persist. Store your lens in a poly bag with a bag of desiccant, and over time, it should draw out any internal moisture, though it might take a while. In any case, a dew heater is worth a try.

Moisture in the lens is caused by bringing a cold lens into a heated environment without bagging. Moisture in that environment will condense on the cold surfaces and any air drawn into the lens will bring moisture with it. It's good practice to bag a lens with desiccant which will prevent moisture from accumulating in your lens.

Bob,

My apologies - I wasn't clear. By "cooler air," I meant that I am going from inside (about 72) to outside, cooler (fall) air, at about 35-50 degrees F, depending on evening.

At any rate, condensation would not seem to be an issue going from warm inside to cool outside air.

However, I will also bag (Ziplock Feezer bag?) my lens with some desiccant packs (silca gel) I have, to try to wick any moisture.

[angerdan]

I have the Tamron A001, which is a very decent lens, all around. Recently, in doing astro images, the group (and I) noted that there was serious vignetting going on in the images. I do not notice it in single shots, but in multiple / stacking, it definitely becomes a thing.
I was wondering if performing an operation similar to this: Modifying the DA* 60-250mm F4 for Full Frame - Introduction - In-Depth Articles might result in better images?

Since your Tamron 70-200mm F2.8 Di LD Macro is an full frame lens, there could be no regular vignetting.
Tamron 70-200mm F2.8 Di LD Macro Lens Reviews - Tamron Lenses - Pentax Lens Review Database

What happens when you shoot images on earth in daylight?

[BigMackCam]

Since your Tamron 70-200mm F2.8 Di LD Macro is an full frame lens, there could be no regular vignetting.
Tamron 70-200mm F2.8 Di LD Macro Lens Reviews - Tamron Lenses - Pentax Lens Review Database

I believe the OP is describing what he believes to be "light fall-off" rather than "physical obstruction" vignetting - and you'd certainly expect some light fall-off with most full-frame lenses on a full-frame camera at wider apertures...

[slartibartfast01]

All,



I have the Tamron A001, which is a very decent lens, all around. Recently, in doing astro images, the group (and I) noted that there was serious vignetting going on in the images. I do not notice it in single shots, but in multiple / stacking, it definitely becomes a thing.



Now, I notice that there is a baffle at the end of the lens. I was going to post some photos, but realized that the old sale ad here has some excellent examples of the baffle.



I was wondering if performing an operation similar to this: Modifying the DA* 60-250mm F4 for Full Frame - Introduction - In-Depth Articles might result in better images?



The Canon, Nikon, and Sony mount versions of this lens do not have the baffle in place. Pentax versions on eBay and here show the baffle. I have attached a sample showing the vignetting - it happens with and without the 1.4x TC.







Thoughts?



--Jonathan

Is that image processed or straight from the camera?

[Bob 256]

Bob,

My apologies - I wasn't clear. By "cooler air," I meant that I am going from inside (about 72) to outside, cooler (fall) air, at about 35-50 degrees F, depending on evening.

At any rate, condensation would not seem to be an issue going from warm inside to cool outside air.

However, I will also bag (Ziplock Feezer bag?) my lens with some desiccant packs (silca gel) I have, to try to wick any moisture.

It goes against logic, but if the air outside has enough moisture, equipment will act like a magnet, condensing that moisture onto their surfaces once the equipment cools down to the outside temperature. It's not a problem while the equipment is still warm from being inside, but after it cools. That's why a dew heater works, it keeps the equipment above the "dew point" of the surrounding air. If the air is dry, this won't happen, so really cold outside environments (significantly below freezing) where all the moisture has frozen out, won't present much of a problem. In any case, a dew heater is a good idea when you have this problem, and keeps your equipment from fogging unless the environment is really saturated with moisture (think foggy day).

The other thing that's bad is that as your lens or equipment cools, any air spaces in it will cool and the air therein will shrink drawing the outside air into the equipment. That might explain why you can get fog inside a lens over time unless the lens is sealed completely air tight (not usually the case for technical reasons). Bagging equipment can keep this from happening, but the desiccant will draw out this moisture given time.

[stevebrot]

I would not blame the baffle. That is a FF compatible lens. I suspect BMC is correct that there is serious loss of contrast in the center, not vignette in the corners.

Edit: I just read the comment above, condensation is a very real possibility with the "vignette" being the shadow of the lens hood, perhaps.


Steve

[jawats]

Since your Tamron 70-200mm F2.8 Di LD Macro is an full frame lens, there could be no regular vignetting.
Tamron 70-200mm F2.8 Di LD Macro Lens Reviews - Tamron Lenses - Pentax Lens Review Database

What happens when you shoot images on earth in daylight?

I do not see any issue with images in daylight. I'm fairly happy with bird, nature, landscape, etc. photos. However, I am wondering if the stacking accentuates vignetting that is not otherwise noticeable in "normal" photos.

---------- Post added 11-08-21 at 04:18 PM ----------

Is that image processed or straight from the camera?

The original image is both processed (stacked some 90 images) and not processed (nothing other than stacking is going on).

---------- Post added 11-08-21 at 04:19 PM ----------

It goes against logic, but if the air outside has enough moisture, equipment will act like a magnet, condensing that moisture onto their surfaces once the equipment cools down to the outside temperature. It's not a problem while the equipment is still warm from being inside, but after it cools. That's why a dew heater works, it keeps the equipment above the "dew point" of the surrounding air. If the air is dry, this won't happen, so really cold outside environments (significantly below freezing) where all the moisture has frozen out, won't present much of a problem. In any case, a dew heater is a good idea when you have this problem, and keeps your equipment from fogging unless the environment is really saturated with moisture (think foggy day).

The other thing that's bad is that as your lens or equipment cools, any air spaces in it will cool and the air therein will shrink drawing the outside air into the equipment. That might explain why you can get fog inside a lens over time unless the lens is sealed completely air tight (not usually the case for technical reasons). Bagging equipment can keep this from happening, but the desiccant will draw out this moisture given time.

I'm not sure it's against logic - just against expectations. :P

How much time in a bag would you think would be necessary to balance out moisture?

---------- Post added 11-08-21 at 04:20 PM ----------

I would not blame the baffle. That is a FF compatible lens. I suspect BMC is correct that there is serious loss of contrast in the center, not vignette in the corners.

Edit: I just read the comment above, condensation is a very real possibility with the "vignette" being the shadow of the lens hood, perhaps.


Steve

Shadow of the lens hood?

Always more variables, lol.

Perhaps I'll try this sans hood sometime. Maybe when I can cause a neighborhood power outage to create some nice dark skies. :P

[slartibartfast01]

I do not see any issue with images in daylight. I'm fairly happy with bird, nature, landscape, etc. photos. However, I am wondering if the stacking accentuates vignetting that is not otherwise noticeable in "normal" photos.

---------- Post added 11-08-21 at 04:18 PM ----------





The original image is both processed (stacked some 90 images) and not processed (nothing other than stacking is going on).

---------- Post added 11-08-21 at 04:19 PM ----------





I'm not sure it's against logic - just against expectations.



How much time in a bag would you think would be necessary to balance out moisture?

---------- Post added 11-08-21 at 04:20 PM ----------





Shadow of the lens hood?



Always more variables, lol.



Perhaps I'll try this sans hood sometime. Maybe when I can cause a neighborhood power outage to create some nice dark skies. :P

Did you include flats when you stacked the images? They should take care of vignetting.

[UncleVanya]

Let me point out that if you don’t correct each shot any uneven illumination the differences add up and can increase the effect depending on the method of stacking.