Anyone ever successfully use a teleconvertor with unsupported lenses?

[misterjones]

To the OP.
The 75-300 may work with a 1.4x TC but will be near unusable with a 2x.
300mm is not a bad focal length but not knowing what you need the extra focal length for it's hard to really make a recommendation.

Sorry it took so long for me to see this.

The bulk of my photography centers around nature and whatever animals I see. Given that I use an APS-C body, I know I've been getting ~480mm our of my 75-300 and now Tamron 70-300mm lenses however there are times where I need more than that. Price-wise, a 600mm lens is out of my reach, as are lenses that tap out at 400mm. I have a "super zoom" bridge camera that hits an adjusted 576mm, but image quality suffers out that far. I live in a somewhat rural area so there's deer, beaver, woodchuck, and a myriad of other woodland creatures that I spot randomly just going to the gym. If I happen to have one of my cameras with me (which is more often the case than not) and I have the ability to stop to catch a shot, I'll do that. Sometimes they're so far away that even my super zoom bridge camera can't get a good shot, so to have a teleconvertor to use with one of my longer lenses would be a huge help when trying to get a shot.

This is an example: I caught these deer in a field on the way home from the gym one weekend a bit over a month ago.

I took this with the Tamron 70-300mm lens. If I had a teleconvertor that would work with this lens, I believe could have got a better shot with more detail.

 

[petrochemist]

Sorry it took so long for me to see this.

The bulk of my photography centers around nature and whatever animals I see. Given that I use an APS-C body, I know I've been getting ~480mm our of my 75-300 and now Tamron 70-300mm lenses however there are times where I need more than that. Price-wise, a 600mm lens is out of my reach, as are lenses that tap out at 400mm. I have a "super zoom" bridge camera that hits an adjusted 576mm, but image quality suffers out that far. I live in a somewhat rural area so there's deer, beaver, woodchuck, and a myriad of other woodland creatures that I spot randomly just going to the gym. If I happen to have one of my cameras with me (which is more often the case than not) and I have the ability to stop to catch a shot, I'll do that. Sometimes they're so far away that even my super zoom bridge camera can't get a good shot, so to have a teleconvertor to use with one of my longer lenses would be a huge help when trying to get a shot.

This is an example: I caught these deer in a field on the way home from the gym one weekend a bit over a month ago.

View attachment 282795

I took this with the Tamron 70-300mm lens. If I had a teleconvertor that would work with this lens, I believe could have got a better shot with more detail.

I have a couple of mirror lenses that might work to get closer in such cases.
One is a 500mm/5.6 and the other a 600mm/8
Neither was even near £100, but they are manual focus so can be tricky to get right. When I tried the 600 on MFT (1200mm equivalent) I found framing nearly impossible without a monopod due to the very narrow FOVv. I have successfully handheld it at 900mm equivalent which is what it would give on your body.

FWIW I also have a MTO 1000mm/11, but thats a much heavier beast that really needs a tripod not something I'd take around for a grab shot.

 

[zombiesniper]

I would recommend seeing if you can get to a camera store if possible and see if they will let you put a TC on your current set up (in store) to see if it will be sharp enough. The camera shop near me is really good for this and it's how I've bought used gear in the past.