sharisujka Loc: Winter Park, FL

I have a Nikon Z-50 that I use the adaptor that I bought when I purchased the camera with a Sigma 600mm lens.
I have no problems with that setup but I would like to go to an 800mm lens because my interest is in photographing birds, mostly for making identification when I get home if I need to. The 800mm Nikor lens is a bit pricey for me and I was wondering if a teleconvertor would work on that camera with a 400mm lens and get just as good photographs. Anyone have any insight or suggestions about this?

Orphoto Loc: Oregon

Just as good will depend on your personal standards as to good enough. As a general rule a 400 with a 2x converter will not match an 800. Birds in flight are especially taxing on gear. By the way atmospheric heat shimmers are optical killers at greater magnifications.

Paulco2 Loc: Gettysburg PA

While I don't have the same gear you cite, I have used teleconverters with my Nikon camera/lens with no noticeable degradation of quality. The only factor I've had to consider is a one or two Fstop loss of exposure with resultant changes to shutter speed/aperture/ISO settings.

DirtFarmer Loc: Escaped from the NYC area, back to MA

I haven’t used teleconverters for many years but they did result in soft focus back then. However if the purpose is only identification that should not be a big deal. OTOH I don’t believe going from 600 to 800 will really get you very far.

MrPhotog

Since you have the 600, why not get a high quality 1.4x converter? The combination will be a bit more than 800 mm, and you’ll lose just 1 stop.

It should be about the same price as a 2x converter alone.

You’ll save the cost of buying a 400 mm lens, which would lose 2 stops with the 2x converter.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

There is not a teleconverter made that improves an image, so, there is only one way to go with a teleconverter, and it's not a good thing.
Look, your Z-50 is an aps-c camera, so any ff lens you put on it will automatically get a bump in field of view.
So, put a prime 400 on your camera, and it becomes a field of view of 600 mm WITHOUT a teleconverter.
My suggestion, try the 400 on your Z-50, my most telephoto lens is a 600 prime, I do wildlife professionally, I need nothing more than that for 99% of my work.
800mm entails a lot of expert handling to assure a strong sharp image.
Do us all a favor and put your money into a 400 or 500 prime and do not pass go, and do not purchase a teleconverter.
BETTER SUGGESTION
Buy the Nikon 180-600, this lens will give you a field of view of 270-900mm. You will not ever need anything else for wildlife photography, this lens is much sharper than any Sigma lens on the market in a similiar focal length.
Read the reviews on the Nikon 180-600, they are very good for a lens under 2 grand.
Plus, a zoom is more versatile than a fixed prime.
In the field I use the Sony 200-600 for much of my work, I do have a 600 prime but within a 100 yards, it is really hard to tell the difference between the two.
Below is an image with the 200-600.
If I were you I would consider this lens, the Nikon 180-600 as your go to wildlife lens.
Good luck and keep on shooting until the end.

Jimmy T Loc: Virginia

This may make it easy to do . . . https://www.bhphotovideo.com/c/search?Ntt=nikon%20nikkor%20z%20180-600mm%20f%2F5.6-6.3%20vr%20lens&N=0&InitialSearch=yes&sts=ps
Best Wishes,
JimmyT Sends

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

That was one of my recommendations.

Retired CPO Loc: Travel full time in an RV

I agree about teleconverters. I tried them back in the day with film. Was NOT impressed! Never saw one that improved optics! I've heard that modern versions are better, but I will stick with the primary lens. Note that I didn't say PRIME! I like good quality ZOOMS!

cjc2 Loc: Hellertown PA

I have used Teleconverters (TC) over the years and while they do increase the magnification, they increase a lot of bad things as well. Generally speaking, a lens without a TC will render a sharper image than the same lens with one. The latest F Mount TCs were much better than the older ones, but the same statement applies. I have now switched to ALL Z Mount and don't even own, and have never tried, a Z TC so I can't comment. I will say that my 400/2.8Z with the built in TC is nothing short of amazing and I would assume that to be true because it was made specifically for that lens. As a sports shooter the 400 is my most used lens, and the one I used TCs on the most in past versions. Having one built in is mind-blowing! Best of luck.

Toment Loc: FL, IL

A 400 mm lens is a 400 mm lens. The TC only gives a crop. It is not the same.

Jimmy T Loc: Virginia

That was my point.
I concur with your recommendation . . .
I was just providing the link to your advice to make it easier for sharisujka to investigate/follow your advice.
I didn't mean to step on any toes.
JimmyT Sends

whatdat Loc: Del Valle, Tx.

At least on Nikons, tc’s are not compatible with most Nikon zooms. Back in the film days I did use a 2x tc on a 70-210 Nikon lens with good results processed as slides.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

No toes stepped on. We are good.

MJPerini

Most manufacturers make recommendations about which lenses work best with TC's
Many of the long prime telephotos work quite well, Zooms a little less so because the TC's can't be optimized for every focal length and also because of the sheer number of optical components involved.
But some zooms like the 70-200 seem to work well. If you can get there with the 1.4 converter all the better.
Pay particular attention to stability and damping.
I remember reading an article by Moose Petersen (who uses converters all the time) uses a heavy tripod and the "Arm drape technique" where he rests an arm over the lens (DEAD ARM STYLE) to help damp vibrations .
Because lots of the teleconverter's bad rap for sharpness comes from vibration. He does all kinds of wildlife and Air to Air vintage plane shots.