Canon 800D - new lens or new body?

Goggatjie wrote:

Advice required please (bit of a long one... sorry)...

I have a Canon 800D and have around £750 to spend but not sure what to buy next. I enjoy macro photography as well as night sky, landscapes, birds and nature. I wanted my next lens to either be a Canon 100mm macro (means I’ll need to wait till later next year when I have enough saved) or the sigma 150 600 which will give me that extra reach for photographing birds and nature which I can purchase sooner.
I have had my eye on the Sigma 150-600 contemporary. What are your thoughts on this lens with a crop sensor bearing in mind that at 600mm there is no auto auto focus at f8 with this camera body? Is it overkill on a crop sensor (x1.6)...?

My second question is this... I really love night photography but find it incredibly difficult with my current arrangement (Canon kit 18-55 & 55-250, 50mm f1.8 and canon 10-18mm ef-s). Part of me wishes that I had saved more to start with and purchased a full frame camera for better low light photography as well as better overall features & control that cameras like the 5dmk3 offer. Also more future proof in terms of abilities. I know that I need better lenses but money is tight (it took ages to save £750 and the wife is adamant this hobby is to be funded via monthly trickle savings) and I am now wondering if I should rather flog my 800D and lenses (keeping the 50mm) and buy a used 5dmk3 (they go for around £750 with low shutter count) If I do that I might just be able to stretch and buy the Sigma lens at the same time... Then going forward I can save for decent ef lenses.

Is this a terrible idea or would that £750 be better spent on better lenses for my 800D?

Oh... would to do...? 🧐😬

Sounds like you need to figure out what you really need instead of what you want.  You're kind of all over the map...macro lens, super zoom lens or a body.

I know nothing about super zoom lenses, but the Canon 100mm macro lenses are very nice.

As far as night photography, what is the difficulty you are having. Do you use a tripod?

If not, I wold get that first.  I will make you nigh shots much easier to get and will be handy if you decide to get a macro lens.