TLR newbie, exposure question

Welcome to the forum - and to film! piratebates ... This will be a bit long, but hopefully useful.

The YashicaFlex cameras were released at a time when film speeds were significantly slower, and ISO 400 film wasn't available. The sunny 16 rule may work - with some adjustments - as long as you have an available f-stop to set your aperture to. As you point out, you won't have a 1/400 shutter speed, and could use 1/300 - but - you may run out of aperture choices when using 400 ISO film. Increases in film speed means faster settings to get equivalents, i.e., f/64 instead of f/32.

Here's a link to a manual for the YashicaFlex C. It has an exposure table in it that assumes an ISO of 200. That means that technically, you'd double all your settings to get a faster equivalent if you also set the camera to 200 instead of 300 or 400 when using Sunny 16. An alternative is to 'pull' your film's ISO rating, so that you treat the film as if it were actually ISO 200, and set your exposures to match 200. Your film lab will need to be able to handle 'pull processing' so that they can adjust how they process the film to do the compensation for you. If you haven't already found a list of film labs, or don't know which ones can do push/pull processing, I might have a link or a list of mail-in and local labs to help you find someone.

When I used 'technically' above, that would hold true if settings had to be very precise to make HP5+ work with your camera's limitations when using 400 film. The good news is that HP5+ is a wide latitude film stock, and it will do 2 things in your favor. 1). Handle pull processing without issues, and 2). give you more room to make minor exposure mistakes to still get a good 'print', whether it's for physical paper prints, or for scanning to digital workflows. It might be able to handle 1/2 or even 1 or more full stops of exposure difference, without needing to pull the speed at all. Essentially you might be able to set the camera to 1/300th, and use the Sunny 16 with no adjustments, and still have good prints. Other members here might have had success and can confirm how well it works, but it's not something I've had to do and know from first-hand experience.

More alternatives...

You camera will accept bayonet filters marked as 'Bay 30' or 'Bay 1'. You can get neutral density filters that will compensate exposures by letting in less light. They can be a bit pricey, but they work and come in varying degrees of densities (1/2/3/4/5/6/10 stops), so you can precisely match a wide range of setups. You only need 1 on the taking lens, so you won't see a darker view while composing shots in the viewfinder. (BTW... an effect only possible with TLR's and rangefinders)

If you have a smartphone, load a free light meter app on it. They may not be 100% accurate, but they can give you some idea on where settings need to be, and help to confirm guesses and calculations, or even help with light/shadows tonal ranges - plus - at the very least, they may have tools to help with compensations/calculations when using sunny 16. It can also give you a cheap backup if you later buy a meter, and the batteries die. Do try the app before you start shooting to see if it will work, and rely on user ratings too... some apps are worthless ad revenue generators and are not light meters at all.

Save the 400 film for indoor shooting where you'll definitely appreciate the extra speed, and buy a 100 or 200 ISO film for daylight use. I'd suggest 200 for hand-held shooting to cover both bright and dark scenes. Tripods are magic on a stick when you need a stable platform and no-shake shooting with slower speed film stock on TLR's. You'll want a light meter for indoor use though, unless you have a flash setup to use.