[HanSch]

My Sigma APO EX DG 4/100-300mm has a small fungus spot on the surface of the second lens element and Sigma can't remove it or replace the lens element (out of stock). No problem so far, but if the fungus get worse the lens will be lost. Shame, an excellent lens.

So I consider buying a Pentax 150-450mm. The Sigma came with a dedicated 1.4x TC, that fits only a subset of Sigma lenses. Does anyone know if it works with the 150-450? First, there are mechanical issues, e.g. it doesn't fit my Sigma 17-70mm Contemporary (protruding element in the TC). The 4/100-300mm is a screwdrive lens, but I can't even check the HSM AF of the 17-70mm because I can't mount the TC.
How about the Pentax 150-450mm?

[ramseybuckeye]

I can't answer you question, but maybe UV light could kill the fungus or at least slow it.

[marcusBMG]

Well I had issues mounting a sigma apo 1.4x tc but fixed that by judiciously filing the locking pin on the mount - the tc to lens side. I have just acquired the AF version of the apo tc (with the 300-4 apo) but haven't tried it yet* to see if it has the same issue.
*Just tried it on my DFA 150-450 no problem, clicks on fine, but of course it doesn't have hsm contacts to work with that lens.
Fungus won't spread if the lens is stored correctly. Your one spot is liekly to remain as it is for as long as you have the lens. It would need to really grow and prevade the lens to visibly affect results. Just out of interest, you can put a circular bit of paper say the size of your thumbnail on the front objective of your lens and I bet you still wouldn't notice any difference with the pics...

[HanSch]

I can't answer you question, but maybe UV light could kill the fungus or at least slow it.

Thanks, that is a nice idea. Can give it a try.

---------- Post added Mar 29th, 2023 at 19:43 ----------

Just tried it on my DFA 150-450 no problem, clicks on fine, but of course it doesn't have hsm contacts to work with that lens.Fungus won't spread if the lens is stored correctly. Your one spot is liekly to remain as it is for as long as you have the lens. It would need to really grow and prevade the lens to visibly affect results. Just out of interest, you can put a circular bit of paper say the size of your thumbnail on the front objective of your lens and I bet you still wouldn't notice any difference with the pics...

Thank you, this answers my questions. So the TC fits, inspite of the protruding element, but misses the contacts for the HSM. So it is practically useless.

I agree, that as long as the fungus doesn't spread there will be no problem with IQ. I did a similar test as you propose (some time ago I punched a circular piece out of a post-it paper and sticked it to the lens), and as expected there was no effect. It is the same as with dust in the lens: as long as it is a reasonable amount, you don't see it. The fungus could ruin my lens in the long run, but if I can keep it under control there is no problem.

[marcusBMG]

It's not useless you just wont have autofocus.

[mlag]

My Sigma APO EX DG 4/100-300mm has a small fungus spot on the surface of the second lens element and Sigma can't remove it or replace the lens element (out of stock). No problem so far, but if the fungus get worse the lens will be lost. Shame, an excellent lens.

So I consider buying a Pentax 150-450mm. The Sigma came with a dedicated 1.4x TC, that fits only a subset of Sigma lenses. Does anyone know if it works with the 150-450? First, there are mechanical issues, e.g. it doesn't fit my Sigma 17-70mm Contemporary (protruding element in the TC). The 4/100-300mm is a screwdrive lens, but I can't even check the HSM AF of the 17-70mm because I can't mount the TC.
How about the Pentax 150-450mm?

In addition, I can confirm the new pentax TC 1,4x on the 150-450mm performs excellent...

( "IF" TC still needed, as you jump from 300 to 450mm already... and yes, I put stress on the IF needed at all - as the combo yields 630mm and this is into territory where tele shooting gets more tricky/difficult and handheld teleshooting close to impossible).

[cmohr]

My Sigma APO EX DG 4/100-300mm has a small fungus spot on the surface of the second lens element and Sigma can't remove it or replace the lens element (out of stock). No problem so far, but if the fungus get worse the lens will be lost. Shame, an excellent lens.

As others have comfirmed, the Sigma TC will not give AF capability on the 150-450, The Pentax DA1.4xTC is really good, but an alternative is something like the Kenko/Tamron Pz-AF 1.4xTC it has a set of contacts that were used for the powerzoom function back in the film day, they now work with the AF on newer SDM Pentax lenses.

Another idea with your Sigma 100-300, the Pentax K-mount of this lens has always been expensive due to it's rarity, but Canon and Nikon version can be bought for very little , and maybe a cheep Canikon lens can become a donor lens for the Pentax one you have. Just a thought..

PS, there is also a Sigma 100-300/f4 in the marketplace now, no affiliation with the seller, and if you love the sigma, it could be a way to stick with it, and much cheaper than a 150-450, and or repairs to your current lens.

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Last edited by cmohr; 03-29-2023 at 02:01 PM.

[HanSch]

In addition, I can confirm the new pentax TC 1,4x on the 150-450mm performs excellent...

( "IF" TC still needed, as you jump from 300 to 450mm already... and yes, I put stress on the IF needed at all - as the combo yields 630mm and this is into territory where tele shooting gets more tricky/difficult and handheld teleshooting close to impossible).

Yes, I know. I use a TC2 as well sometimes, and of course this requires a sturdy tripod, remote release or (better) mirror lock-up, and still it is no guarantee for sharp images. LiveView with magnification for MF is practically useless, you touch the lens and the image bounces around. A disadvantage of in-body stabilization as compared to OS.
I don't expect to need a TC2 with 450mm as maximum focal length, but 1.4 might be useful.

---------- Post added Mar 30th, 2023 at 12:25 ----------

It's not useless you just wont have autofocus.

That's correct. Useful for stable, stationary objects, as the 150-450 seems to have excellent MF options.

---------- Post added Mar 30th, 2023 at 12:31 ----------

As others have comfirmed, the Sigma TC will not give AF capability on the 150-450, The Pentax DA1.4xTC is really good, but an alternative is something like the Kenko/Tamron Pz-AF 1.4xTC it has a set of contacts that were used for the powerzoom function back in the film day, they now work with the AF on newer SDM Pentax lenses.

Another idea with your Sigma 100-300, the Pentax K-mount of this lens has always been expensive due to it's rarity, but Canon and Nikon version can be bought for very little , and maybe a cheep Canikon lens can become a donor lens for the Pentax one you have. Just a thought..

.

Just a thought, but an interesting one. You are right, the Canikon versions are more frequent in the used market. And since the important element is inside the lens, it will probably be no objection to cannibalize a heavily used copy. If Sigma is prepared to do the service.