DSR have been scrapped now and your rights are under consumer contract regulations, which has increased the basic right of return to 14 days.
Your specific case would be a bit grey and I’d say ask the question to the company selling the lens for their take on it and get it in writing.
My interpretation would be that if you ordered from Jessops and collected there, you have chance to inspect the goods and refuse them there and then if they didn’t suit so it would be a face to face contract and you would have normal shop rights, I.e. No right to return. If you ordered from Jessops and used something like the click and collect delivery service to Argos then it would be a off premises contract and the right to return would apply. There’s not actually any direct provision for that situation in the law though.
Remember that you’re only checking the goods are as described and having the same ability to test as in a shop – just because you can buy something online doesn’t mean you get 14 days to play with it and send it back if you don’t want it.. You can look at a lens exactly the same way you would in store if you bought online and collected in store, so there would be no need for you to have any additional rights.